Transverse bulk acoustic wave filter

ABSTRACT

A micro-transfer printable transverse bulk acoustic wave filter comprises a piezoelectric filter element having a top side, a bottom side, a left side, and a right side disposed over a sacrificial portion on a source substrate. A top electrode is in contact with the top side and a bottom electrode is in contact with the bottom side. A left acoustic mirror is in contact with the left side and a right acoustic mirror is in contact with the right side. The thickness of the transverse bulk acoustic wave filter is substantially less than its length or width and its length can be greater than its width. The transverse bulk acoustic wave filter can be disposed on, and electrically connected to, a semiconductor substrate comprising an electronic circuit to control the transverse bulk acoustic wave filter and form a composite heterogeneous device that can be micro-transfer printed.

PRIORITY APPLICATION

This application is a Continuation-in-Part of U.S. patent applicationSer. No. 15/047,250, filed Feb. 18, 2016, entitledMicro-Transfer-Printed Acoustic Wave Filter Device, the disclosure ofwhich is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates to integrated heterogeneous structures,and more particularly to an acoustic wave filter micro-transfer printedonto a semiconductor substrate.

BACKGROUND OF THE INVENTION

Electronic circuits are widely used in communication devices. Inparticular, mobile devices that rely upon modulated electromagneticradiation to communicate a signal require filters to remove noise andinterference from received electronic signals and, in particular, toremove frequencies outside a desired range. Such filtering can be donein a variety of ways, for example, with electromechanical filters, withresonant electronic circuits such as tuned resonant tank circuitsincluding various combinations of resistors, capacitors, and inductors,and with digital filters using digital signal processors to filterdigitized electronic signals.

Electromechanical filters have been used extensively in radiocommunications for many decades. One group of such filters depend uponelectromechanical piezoelectric materials that mechanically(acoustically) resonate at a desired frequency and that either respondmechanically to electrical stimulation or produce an electrical signalin response to mechanical stimulation. Electromechanical filters usingpiezoelectric materials are variously known as acoustic filters,acoustic wave filters, acoustic resonators, crystal filters, or crystaloscillators. A variety of useful piezoelectric materials are known. Forexample, quartz has been used for more than 80 years because of its lowcoefficient of thermal expansion and high quality factors.

In recent years, different acoustically resonant modes have beenexploited in piezoelectric materials, including surface acoustic wave(SAW) filters and bulk acoustic wave (BAW) filters. U.S. Pat. No.5,313,177, and U.S. Pat. No. 7,307,369 describe surface acoustic wavedevices. U.S. Pat. No. 5,872,493 teaches a bulk acoustic wave (BAW)filter having a protective acoustic mirror. Acoustic mirrors are alsoknown as reflector layers or acoustic reflectors. Single crystalacoustic resonators (SCARs) are also known, for example, as disclosed inU.S. patent application Ser. No. 14/796,939.

In many applications, for example, mobile communication devices found incellular telephones, size and weight are important device attributes andtherefore electronic circuits are preferably small, light, low cost, andhighly integrated. Electromechanical filters are used as components inelectronic circuits and there is, therefore, a need for improvedintegration of such filters in electronic circuits for telecommunicationdevices.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a compound acoustic wavefilter device comprising a support substrate that can be a semiconductorsubstrate. An acoustic wave filter includes a piezoelectric filterelement and two or more electrodes. The acoustic wave filter ismicro-transfer printed onto the semiconductor substrate. The electrodescan form or be connected to one or more transducers, for example asingle transducer. Alternatively, the electrodes, for example, fourelectrodes can form or be connected to a first transducer for convertinga first electrical signal to an acoustic wave in or on the filterelement and a second transducer for converting the acoustic wave to asecond electrical signal different from the first electrical signal. Oneor more electrical conductors electrically connect one or more of thecircuit connection pads to one or more of the electrodes. Acoustic wavefilters of the present invention can be surface acoustic wave filters orbulk acoustic wave filters and can include a resonant crystallinematerial. As used herein, acoustic wave filters are also filters,electromechanical filters, acoustic filters, acoustic resonators,crystal filters, or crystal oscillators.

In an embodiment, the support substrate is a semiconductor substratehaving an active electronic circuit formed in or on the semiconductorsubstrate and electrically connected to one or more of the circuitconnection pads. The active electronic circuit can control, at least inpart, the acoustic wave filter. The piezoelectric filter element caninclude or be a substrate or layer separate, distinct, and independentfrom the support substrate. The filter element, acoustic wave filter, orthe support substrate can be bare dies.

By micro-transfer printing the acoustic wave filter onto the adhesivelayer and over the support substrate, the compound acoustic wave filterdevice of the present invention is more highly integrated and thereforesmaller and less expensive than alternative designs and can have betterperformance. Thus, the compound acoustic wave filter device of thepresent invention can be packaged in a single package rather than twoseparate packaged devices interconnected on a third substrate such as aprinted circuit board. The filter element can be micro-transfer printedon the adhesive layer and on or over the support substrate or activeelectronic circuit, further reducing the device size and improving thedevice integration. Furthermore, by micro-transfer printing the acousticwave filter onto the adhesive layer and on or over the supportsubstrate, the length and extent of the electrical connections betweenthe support substrate and the filter element are reduced, reducingnoise, increasing operating frequencies and generally increasing thedevice performance, especially for applications requiring relativelyhigh operating frequencies such as are commonly found in mobiletelecommunications systems such as cellular telephones. In a furtherembodiment of the present invention, a plurality of filter elements ismicro-transfer printed on an adhesive layer and adhered to a singlesupport substrate, enabling multiple acoustic wave filter operationswithin a single packaged device, such as a surface-mount device. In anembodiment of the present invention, the support substrate and anyconductors or active electronic circuits on the support substrate areconstructed and processed separately from the piezoelectric filterelement and electrodes.

In a further embodiment of the present invention, an acoustic wavefilter wafer includes a wafer of substrate material having a patternedsacrificial layer forming sacrificial portions on, over, or in thesubstrate material, a surface of the substrate material, the wafer, or asurface of the wafer. The sacrificial portions separate anchors betweenthe sacrificial portions. A piezoelectric acoustic wave filter is formedentirely over each sacrificial portion, the acoustic wave filtercomprising a layer of piezoelectric material and two or more electrodesin or on the piezoelectric material. The portion of each acoustic wavefilter in contact with the sacrificial portion is chemically andselectively etch-resistant so that the contact portion has a chemicalselectivity different from the patterned sacrificial layer.

In a method of the present invention, a support substrate is providedand a piezoelectric filter element is provided and electrodes are formedin or on the filter substrate to form an acoustic wave filter. One ormore filter elements are mounted on the support substrate bymicro-transfer printing and one or more of the circuit connection padsare electrically connected to the one or more electrodes through thefilter connection pads to construct a compound acoustic wave filterdevice.

The acoustic wave filters are made by providing a support wafer, forexample, a glass wafer. A buffer layer is deposited on the support waferand provides a surface on which a piezoelectric layer is formed, forexample by chemical vapor deposition or atomic layer deposition. One ormore electrodes are patterned on the piezoelectric layer. An optionalacoustic mirror layer is optionally formed on the electrode. Asacrificial layer is patterned over the optional mirror layer orelectrode. A source wafer (also referred to as a handle wafer in thisprocess) is provided and adhered to the adhesive layer. The supportwafer and optionally the optional buffer layer are removed and thestructure is arranged to provide a process surface on the piezoelectricfilter layer. In one embodiment (for example to form a bulk acousticwave filter rather than a surface acoustic wave filter), a secondelectrode is patterned on the filter substrate and an optional secondacoustic mirror layer is formed over the electrode. The filter substrateis processed to expose the patterned sacrificial layer, optionaldielectric insulators are patterned to insulate the filter substrate, ifnecessary, and filter connection pads are formed to provide amicro-transfer printable acoustic wave filter.

In another method of the present invention, a sacrificial layer is notformed. Instead, the support wafer and circuit connection pads areadhered to the adhesive layer instead of the source/handle wafer and thesupport wafer and optional buffer layer are removed. In this embodiment,the second electrodes and optional second mirror layer (if present) areformed and patterned directly over the filter elements and over thesupport substrate. This avoids the etching process for the individualacoustic wave filters. This approach is particularly useful if thecompound acoustic wave filter device itself is a micro-transferprintable device having a sacrificial layer in the source wafer or underthe active electronic circuit and etched to form a micro-transferprintable compound acoustic wave filter device using compoundmicro-assembly methods.

In a further embodiment of the present invention, a heterogeneous devicecomprises a first substrate comprising a first material and an activefirst circuit formed in or on the first substrate. The active firstcircuit includes one or more first connection pads connected to theactive first circuit for providing signals to the active first circuitor receiving signals from the active first circuit. A second substrateseparate, distinct, and independent from the first substrate comprises asecond material different from the first material. The second substrateis directly or indirectly micro-transfer printed on or adhered to thefirst substrate and includes two or more electrodes or a second circuitformed in or on the second substrate. The two or more electrodes includetwo or more second connection pads connected to the electrodes or secondcircuit for providing signals or receiving signals from the electrodesor second circuit. One or more electrical conductors electricallyconnect one or more of the first connection pads to one or more of thesecond connection pads. The second substrate can include a second activecircuit that incorporates the electrodes, for example includingtransistors or diodes. The second substrate can be micro-transferprinted directly or indirectly on or over the active first circuit,further reducing the device size and improving the device integration.In a further embodiment of the present invention, a plurality of secondsubstrates is micro-transfer printed onto or adhered to a single firstsubstrate, enabling multiple operations within a single packaged device.The device can be a surface-mount device. In an embodiment of thepresent invention, the active first substrate and first circuit areconstructed and processed separately from the second substrate andelectrodes or second circuit.

Embodiments of the present invention therefore enable devices comprisinga variety of different heterogeneous materials that can each beprocessed or assembled separately using different, possiblyincompatible, processes. By using semiconductor materials in at leastthe first substrate, the devices can incorporate logic circuits, such asstate machines or computers such as digital stored program machines.Thus, embodiments of the present invention provide intelligent, highlyintegrated heterogeneous devices useful in a wide variety ofapplications and modalities.

In one aspect, the disclosed technology includes a compound acousticwave filter device, the device including: a support substrate having twoor more circuit connection pads; an acoustic wave filter comprising apiezoelectric filter element and two or more electrodes on thepiezoelectric filter element; an adhesive layer located between thesupport substrate and the acoustic wave filter, wherein the acousticwave filter is micro-transfer printed on the adhesive layer and theadhesive layer adheres the support substrate to the acoustic wavefilter; and two or more electrical conductors, each electrical conductorelectrically connecting one of the electrodes to one of the circuitconnection pads.

In certain embodiments, the two or more electrodes are formed on acommon side of the piezoelectric filter element and the acoustic wavefilter is a surface acoustic wave filter.

In certain embodiments, the two or more electrodes are formed onopposite sides of the piezoelectric filter element and the acoustic wavefilter is a bulk acoustic wave filter.

In certain embodiments, the acoustic wave filter or the piezoelectricfilter element includes at least a portion of a tether.

In certain embodiments, the piezoelectric filter element has apiezoelectric filter element area that is smaller than the area of thesupport substrate.

In certain embodiments, the acoustic wave filter is directly orindirectly adhered to the support substrate with an adhesive layer.

In certain embodiments, the adhesive is a cured adhesive.

In certain embodiments, the layer of adhesive has an extent over thesupport substrate that is different from the extent of the acoustic wavefilter.

In certain embodiments, the support substrate is a semiconductorsubstrate and comprising an active electronic circuit formed in or onthe semiconductor substrate, the active electronic circuit electricallyconnected to one or more of the circuit connection pads.

In certain embodiments, the active electronic circuit is located atleast partially between the acoustic wave filter and the semiconductorsubstrate.

In certain embodiments, the semiconductor substrate is a siliconsemiconductor substrate, a compound semiconductor substrate, a III-Vsemiconductor substrate, a crystalline material substrate, or acrystalline semiconductor material substrate.

In certain embodiments, the semiconductor substrate has a process side,the electronic circuit is formed on or in the process side, and theacoustic wave filter is micro-transfer printed on the process side.

In certain embodiments, the piezoelectric filter element is asemiconductor, a compound semiconductor, a III-V semiconductor, a II-VIsemiconductor, GaN, AlGaN, a ceramic a synthetic ceramic, galliumorthophosphate (GaPO4), Langasite (La3Ga5SiO14), lead titanate, bariumtitanate (BaTiO3), lead zirconate titanate (Pb[ZrxTil-x]O3 0≦x≦1),potassium niobate (KNbO3), lithium niobate (LiNbO3), lithium tantalate(LiTaO3), sodium tungstate (Na2WO3), Ba2NaNb5O5, Pb2KNb5O15, zinc oxide(ZnO), Sodium potassium niobate ((K,Na)NbO3) (NKN), bismuth ferrite(BiFeO3), Sodium niobate (NaNbO3), bismuth titanate (Bi4Ti3O12), sodiumbismuth titanate (Na0.5Bi0.5TiO3), wurtzite, polyvinylidene fluoride, oraluminum nitride (AlN).

In certain embodiments, the device includes an acoustic mirror layerlocated on a side of one of the electrodes opposite the filter elementwith the filter element between the support substrate and the acousticmirror layer, an acoustic mirror layer located on a side of one of theelectrodes with the acoustic mirror layer between the support substrateand the filter element, or both.

In certain embodiments, at least one of the acoustic mirror layers ischemically etch-resistant.

In certain embodiments, at least one of the electrodes is chemicallyetch resistant.

In certain embodiments, the piezoelectric filter element is thicker thanthe support substrate.

In certain embodiments, the piezoelectric filter element is thinner thanthe support substrate.

In certain embodiments, the support substrate has a thickness less thanor equal to 20 microns, 10 microns, or 5 microns.

In certain embodiments, the piezoelectric filter element has a thicknessless than or equal to 10 microns, 5 microns, or 1 micron.

In certain embodiments, the piezoelectric filter element has a thicknessgreater than or equal to 0.5 microns, 1 micron, 2 microns, or 5 microns.

In certain embodiments, the electrodes form a plurality of electrodepairs on or in the filter element, and wherein each of the electrodes isconnected to a circuit connection pad with an electrical conductor.

In certain embodiments, the device includes a plurality of the acousticwave filters micro-transfer printed on the adhesive layer, wherein eachelectrode of each of the piezoelectric filter elements is connected to acircuit connection pad with an electrical conductor and, optionally,wherein two or more of the circuit connection pads are electricallyconnected on the support substrate.

In certain embodiments, a first acoustic wave filter of the plurality ofacoustic wave filters has one or more first attributes, a secondacoustic wave filter of the plurality of acoustic wave filters has oneor more second attributes and wherein at least one of the firstattributes is different from at least one of the second attributes.

In certain embodiments, the compound acoustic wave filter device or thesupport substrate has a length or breadth dimension of less than orequal to 1 mm, less than or equal to 800 μm, less than or equal to 600μm, less than or equal to 400 μm, less than or equal to 200 μm, lessthan or equal to 100 μm, less than or equal to 50 μm, or less than orequal to 20 μm.

In certain embodiments, the compound acoustic wave filter device is asurface-mount device.

In certain embodiments, the support substrate or piezoelectric filterelement has at least one of a width from 2 to 5 μm, 5 to 10 μm, 10 to 20μm, or 20 to 50 μm, a length from 2 to 5 μm, 5 to 10 μm, 10 to 20 μm, or20 to 50 μm, and a height from 2 to 5 μm, 4 to 10 μm, 10 to 20 μm, or 20to 50 μm.

In certain embodiments, at least two of the electrodes define capacitorsthat form an electrical or magnetic field when an electrical potentialis applied to the two electrodes causing an acoustic wave in thepiezoelectric filter element. Alternatively, the capacitors can behigh-density capacitors that store energy as an electric field or as anelectrical charge.

In certain embodiments, at least two of the electrodes define capacitorsthat form an electrical signal in response to an electrical or magneticfield provided by the piezoelectric filter element.

In certain embodiments, the electrical conductors are electricallyconductive protrusions or spikes extending from the acoustic wavefilter, a portion or layer of the acoustic wave filter, or the filterelement.

In another aspect, the disclosed technology includes a method of makinga compound acoustic wave filter device, including: providing a supportsubstrate having two or more circuit connection pads; providing anacoustic wave filter, the acoustic wave filter comprising apiezoelectric filter element and two or more electrodes in or on thepiezoelectric filter element; providing an adhesive layer locatedbetween the support substrate and the acoustic wave filter;micro-transfer printing the acoustic wave filter onto the adhesive layerand adhering the support substrate to the acoustic wave filter; andelectrically connecting each of the electrodes to one or more of thecircuit connection pads with electrical conductors.

In certain embodiments, the support substrate is a semiconductorsubstrate, and comprising providing the semiconductor substrate with anactive electronic circuit formed in or on the semiconductor substrate,the active electronic circuit electrically connected to one or more ofthe circuit connection pads.

In certain embodiments, the active electronic circuit is located atleast partially between the acoustic wave filter and the semiconductorsubstrate.

In certain embodiments, the semiconductor substrate has a process side,the active electronic circuit is formed on or in the process side, andthe acoustic wave filter is micro-transfer printed on the process side.

In certain embodiments, the adhesive is a curable adhesive and themethod comprises curing the adhesive layer to adhere the acoustic wavefilter to the support substrate after the acoustic wave filter ismicro-transfer printed onto the adhesive layer.

In certain embodiments, the electrical conductors are electricallyconductive protrusions or spikes extending from the acoustic wave filteror the filter element, and comprising pressing the electricallyconductive protrusions or spikes against, into, or through the circuitconnection pads to form an electrical connection between the electrodesand the circuit connection pads.

In certain embodiments, the method includes providing four or moreelectrodes on the filter element forming two or more acoustic wavefilters on the filter element; and electrically connecting each of theelectrodes to one or more of the circuit connection pads with theelectrical conductors.

In certain embodiments, the method includes providing a plurality ofacoustic wave filters having a corresponding plurality of filterelements;

micro-transfer printing the plurality of acoustic wave filters andfilter elements onto the adhesive layer; and

electrically connecting each of the electrodes of each of the filterelements to one or more of the circuit connection pads with theelectrical conductors.

In certain embodiments, a first acoustic wave filter of the plurality ofacoustic wave filters has one or more first attributes, a secondacoustic wave filter of the plurality of acoustic wave filters has oneor more second attributes, and wherein at least one of the firstattributes is different from at least one of the second attributes.

In certain embodiments, the method includes providing a first acousticwave filter wafer having first acoustic wave filters, a second acousticwave filter wafer having second acoustic wave filters, and whereinmicro-transfer printing the plurality of acoustic wave filters andfilter elements onto the adhesive layer includes micro-transfer printingfirst acoustic wave filters from the first acoustic wave filtersubstrate and micro-transfer printing second acoustic wave filters fromthe second acoustic wave filter substrate.

In certain embodiments, the first acoustic wave filters of the acousticwaver filter wafer have one or more first attributes, the secondacoustic wave filters of the second acoustic waver filter wafer have oneor more second attributes, and wherein at least one of the firstattributes is different from at least one of the second attributes.

In certain embodiments, the filter element has an area that is smallerthan the area of the support substrate.

In certain embodiments, the filter element is a semiconductor, acompound semiconductor, a III-V semiconductor, a II-VI semiconductor, aceramic, GaN, AlGaN, a synthetic ceramic, gallium orthophosphate(GaPO4), Langasite (La3Ga5SiO14), lead titanate, barium titanate(BaTiO3), lead zirconate titanate (Pb[ZrxTil-x]O3 0≦x≦1), potassiumniobate (KNbO3), lithium niobate (LiNbO3), lithium tantalate (LiTaO3),sodium tungstate (Na2WO3), Ba2NaNb5O5, Pb2KNb5O15, zinc oxide (ZnO),Sodium potassium niobate ((K,Na)NbO3) (NKN), bismuth ferrite (BiFeO3),Sodium niobate (NaNbO3), bismuth titanate (Bi4Ti3O12), sodium bismuthtitanate (Na0.5Bi0.5TiO3), wurtzite, polyvinylidene fluoride, oraluminum nitride (AlN).

In certain embodiments, the support substrate is a semiconductorsubstrate, a silicon semiconductor substrate, a compound semiconductorsubstrate, or a III-V semiconductor substrate.

In certain embodiments, the support substrate is a crystallinesemiconductor substrate.

In certain embodiments, the filter element is a crystalline or ceramicpiezoelectric material substrate.

In certain embodiments, the filter element is chemically etch-resistant.

In certain embodiments, at least one of the electrodes is chemicallyetch-resistant.

In certain embodiments, the method includes disposing an acoustic mirrorlayer on a side of one of the electrodes opposite the filter element ordisposing an acoustic mirror layer on a side of each of the electrodesopposite the filter element.

In certain embodiments, at least one of the acoustic mirror layers ischemically etch-resistant.

In certain embodiments, the filter element is thicker than the supportsubstrate.

In certain embodiments, the filter element is thinner than the supportsubstrate.

In certain embodiments, the support substrate has a thickness of lessthan or equal to 20 microns, 10 microns, or 5 microns.

In certain embodiments, the filter element has a thickness less than orequal to 10 microns, 5 microns, or 1 micron.

In certain embodiments, the filter element has a thickness greater thanor equal to 0.5 microns, 1 micron, 2 microns, or 5 microns.

In certain embodiments, the support substrate or filter element has atleast one of a width from 2 to 5 μm, 5 to 10 μm, 10 to 20 μm, or 20 to50 μm, a length from 2 to 5 μm, 5 to 10 μm, 10 to 20 μm, or 20 to 50 μm,and a height from 2 to 5 μm, 4 to 10 μm, 10 to 20 μm, or 20 to 50 μm.

In certain embodiments, the compound acoustic wave filter device is asurface-mount device.

In another aspect, the disclosed technology includes an acoustic wavefilter wafer, including: a source wafer of substrate material; apatterned sacrificial layer forming sacrificial portions on, over, or inthe substrate material, a surface of the substrate material, the sourcewafer, or a surface of the source wafer, the sacrificial portionsdefining separate anchors between the sacrificial portions; apiezoelectric acoustic wave filter formed entirely over each sacrificialportion, the acoustic wave filter comprising (i) a layer ofpiezoelectric material and (ii) two or more electrodes in or on thepiezoelectric material; and wherein the portion of the acoustic wavefilter in contact with the sacrificial portion is chemically andselectively etch-resistant so that the contact portion has a chemicalselectivity different from the patterned sacrificial layer and whereinthe piezoelectric acoustic wave filter is attached to the anchor with atleast one tether.

In certain embodiments, the contact portion is a portion of the layer ofpiezoelectric material or all of or a portion of an electrode.

In certain embodiments, the wafer including one or more acousticmirrors, each acoustic mirror disposed on a side of an electrodeopposite the layer of piezoelectric material, and wherein the contactportion is an acoustic mirror.

In certain embodiments, the patterned sacrificial layer is a patternedlayer of etchable material or a gap between the etch-resistant acousticfilter structure and the substrate material.

In another aspect, the disclosed technology includes a method of makingan acoustic wave filter wafer, the method including: providing a supportwafer and forming an optional buffer layer on the support wafer; forminga piezoelectric material element on the buffer layer or the supportwafer; forming an electrode on the piezoelectric material element; andforming a patterned sacrificial layer on or over the electrode.

In certain embodiments, the method includes forming an adhesive layer onor over the patterned sacrificial layer; providing a source wafer; andadhering the source wafer to the patterned sacrificial layer with theadhesive layer.

In certain embodiments, the adhesive layer is curable and comprisingonly curing the adhesive layer.

In certain embodiments, the method includes removing the support waferand optionally removing the optional buffer layer.

In certain embodiments, the method includes etching the patternedsacrificial layer to form a micro-transfer printable acoustic wavefilter.

In certain embodiments, the electrode is a first electrode andcomprising forming one or more second electrodes on the same side of thepiezoelectric material element as the first electrode, to form amicro-transfer printable surface acoustic wave filter.

In certain embodiments, the method includes forming an acoustic mirroron or over the electrode.

In certain embodiments, the electrode is a first electrode andcomprising forming a second electrode on a side of the piezoelectricmaterial element opposite the first electrode, to form a micro-transferprintable bulk acoustic wave filter.

In certain embodiments, the method includes forming an acoustic mirroron or over the second electrode.

In some embodiments, a micro-transfer printable transverse bulk acousticwave filter comprises a piezoelectric filter element having a top side,a bottom side, a left side, and a right side disposed over a sacrificialportion on a source substrate. A top electrode is in contact with thetop side and a bottom electrode is in contact with the bottom side. Aleft acoustic mirror is in contact with the left side and a rightacoustic mirror is in contact with the right side. The thickness of thetransverse bulk acoustic wave filter is substantially less than itslength or width and its length can be greater than its width. Thetransverse bulk acoustic wave filter can be disposed on, andelectrically connected to, a semiconductor substrate comprising anelectronic circuit to control the transverse bulk acoustic wave filterand form a composite heterogeneous device that can be micro-transferprinted.

In some embodiments of the present invention, the piezoelectric filterelement has a front side and a back side and comprises a front acousticmirror in contact with the front side. A back acoustic mirror is incontact with the back side. In other embodiments, a bottom acousticmirror is in contact with the bottom electrode and optionally in contactwith at least a portion of the bottom side or a top acoustic mirror isin contact with the top electrode and optionally in contact with atleast a portion of the top side, or both.

In some embodiments, the distance between the top side and the bottomside is less than the distance between the left side and the right sideor is less than or equal to one half, one quarter, one tenth, onetwentieth, one fiftieth, 1/100, or 1/200 of the distance between theleft side and the right side. The distance between the top side and thebottom side can be less than the distance between the front side and theback side or less than or equal to one half, one quarter, one tenth, onetwentieth, one fiftieth, 1/100, or 1/200 of the distance between thefront side and the back side. The distance between the front side andthe back side can be less than the distance between the left side andthe right side or less than or equal to one half, one third, onequarter, one tenth, or one twentieth of the distance between the leftside and the back side. A cross section of the piezoelectric filterelement can be substantially rectangular, either taken through the widthor the length of the piezoelectric filter element.

According to some embodiments of the present invention, a voltageapplied across the top and bottom electrodes forms a resonant acousticwave in the piezoelectric filter element that constructively interferesbetween the left and right acoustic mirrors. In further embodiments, afront acoustic mirror is in contact with the front side and a backacoustic mirror is in contact with the back side, and the appliedvoltage forms a resonant acoustic wave in the piezoelectric filterelement that constructively interferes between the front and backacoustic mirrors. In other embodiments, the piezoelectric filter elementhas a top acoustic mirror in contact with the top electrode and a bottomacoustic mirror in contact with the bottom electrode and the appliedvoltage forms a resonant acoustic wave in the piezoelectric filterelement that constructively interferes between the top and bottomacoustic mirrors.

In some embodiments of the transverse bulk acoustic wave filter, a topelectrical conductor is in electrical contact with the top electrode anda bottom electrical conductor is in contact with the bottom electrodeand either the top electrical conductor is disposed at least partiallyon, in, or as part of the left acoustic mirror and the bottom electricalconductor is disposed at least partially on, in, or as part of the rightacoustic mirror, or the top electrical conductor is insulated from theleft side by a dielectric structure that forms at least a portion of theleft acoustic mirror and the bottom electrical conductor is insulatedfrom the right acoustic mirror by a dielectric structure that forms atleast a portion of the right acoustic mirror.

The transverse bulk acoustic wave filter can comprise a fractured orseparated (disengaged) tether disposed under the bottom electrode or ina common plane with the top or bottom electrodes or the piezoelectricfilter element or a layer above or below the piezoelectric filterelement.

In some embodiments of the transverse bulk acoustic wave filter, asupport substrate has top and bottom circuit connection pads, the bottomelectrode is adhered to the support substrate, the top circuitconnection pad is electrically connected to the top electrode, and thebottom circuit connection pad is electrically connected to the bottomelectrode, for example through electrical conductors. The supportsubstrate can be a semiconductor substrate having an active electroniccircuit formed in or on the semiconductor substrate. In an embodiment,the active electronic circuit is electrically connected to the top andbottom circuit connection pads and can be disposed at least partiallybetween the piezoelectric filter element and the support substrate.

In some embodiments, the piezoelectric filter element is a firstpiezoelectric filter element and the transverse bulk acoustic wavefilter comprises a second piezoelectric filter element. The top andbottom electrodes of the second piezoelectric filter element areelectrically connected to the active electronic circuit.

In some embodiments of the present invention, a transverse acoustic wavefilter wafer comprises a source wafer comprising substrate material anda patterned sacrificial layer forming sacrificial portions on, over, orin the substrate material, a surface of the substrate material, thesource wafer, or a surface of the source wafer. The sacrificial portionsdefine separate anchors between the sacrificial portions. A transversebulk acoustic wave filter is disposed entirely over each sacrificialportion and can be formed in place using photolithographic methods andmaterials.

In some embodiments, a transverse acoustic wave filter wafer comprises adevice wafer comprising substrate material having a patternedsacrificial layer forming sacrificial portions on, over, or in thesubstrate material, a surface of the substrate material, the devicewafer, or a surface of the device wafer. The sacrificial portions defineseparate anchors between the sacrificial portions. A transverse bulkacoustic wave filter is disposed entirely over each sacrificial portion,the transverse bulk acoustic wave filter having a fractured or separatedtether. An electrical connection is electrically connected to the topelectrode and an electrical connection is electrically connected to thebottom electrode. In some embodiments, the acoustic wave filter wafercomprises a semiconductor layer disposed entirely over each sacrificialportion between the sacrificial portion and the transverse bulk acousticwave filter, the semiconductor layer having an active electronic circuitto which the electrical connections are electrically connected.

In another aspect, the disclosed technology includes a transverse bulkacoustic wave filter, comprising: a piezoelectric filter element havinga top side, a bottom side, a left side, and a right side, wherein theright side is opposed to the left side and the bottom side is opposed tothe top side; a top electrode in contact with the top side; a bottomelectrode in contact with the bottom side; a left acoustic mirror incontact with the left side; and a right acoustic mirror in contact withthe right side.

In certain embodiments, the piezoelectric filter element has a frontside and a back side, and comprising: a front acoustic mirror in contactwith the front side; and a back acoustic mirror in contact with the backside.

In certain embodiments, the wave filter comprises: a bottom acousticmirror in contact with the bottom electrode and, optionally, in contactwith at least a portion of the bottom side. In certain embodiments, thewave filter comprises a top acoustic mirror in contact with the topelectrode and, optionally, in contact with at least a portion of the topside.

In certain embodiments, the distance between the top side and the bottomside is less than the distance between the left side and the right sideor is less than or equal to one half, one quarter, one tenth, onetwentieth, one fiftieth, 1/100, or 1/200 of the distance between theleft side and the right side. In certain embodiments, the piezoelectricfilter element has a front side and a back side, and wherein thedistance between the top side and the bottom side is less than thedistance between the front side and the back side or is less than orequal to one half, one quarter, one tenth, one twentieth, one fiftieth,1/100, or 1/200 of the distance between the front side and the backside. In certain embodiments, the distance between the front side andthe back side is less than the distance between the left side and theright side or is less than or equal to one half, one third, one quarter,one tenth, or one twentieth of the distance between the left side andthe back side.

In certain embodiments, a cross section of the piezoelectric filterelement is substantially rectangular.

In certain embodiments, a voltage applied across the top and bottomelectrodes forms a resonant acoustic wave in the piezoelectric filterelement between the left and right acoustic mirrors.

In certain embodiments, the piezoelectric filter element has a frontside and a back side, the transverse bulk acoustic wave filter comprisesa front acoustic mirror in contact with the front side and a backacoustic mirror in contact with the back side, and wherein the appliedvoltage forms a resonant acoustic wave in the piezoelectric filterelement between the front and back acoustic mirrors. In certainembodiments, the piezoelectric filter element has a top acoustic mirrorin contact with the top electrode and a bottom acoustic mirror incontact with the bottom electrode and wherein the applied voltage formsa resonant acoustic wave in the piezoelectric filter element between thetop and bottom acoustic mirrors.

In certain embodiments, the wave filter comprises a top electricalconductor in electrical contact with the top electrode and a bottomelectrical conductor in contact with the bottom electrode, and whereinthe top electrical conductor is disposed at least partially on, in, oras part of the left acoustic mirror and the bottom electrical conductoris disposed at least partially on, in, or as part of the right acousticmirror, or wherein the top electrical conductor is insulated from theleft side by a dielectric structure that forms at least a portion of theleft acoustic mirror and the bottom electrical conductor is insulatedfrom the right acoustic mirror by a dielectric structure that forms atleast a portion of the right acoustic mirror.

In certain embodiments, the wave filter comprises a fractured orseparated tether.

In certain embodiments, the wave filter comprises a support substratecomprising top and bottom circuit connection pads and wherein the bottomelectrode is adhered to the support substrate, the top circuitconnection pad is electrically connected to the top electrode, and thebottom circuit connection pad is electrically connected to the bottomelectrode.

In certain embodiments, the support substrate is a semiconductorsubstrate and further comprising an active electronic circuit formed inor on the semiconductor substrate, the active electronic circuitelectrically connected to the top and bottom circuit connection pads. Incertain embodiments, the active electronic circuit is disposed at leastpartially between the piezoelectric filter element and the supportsubstrate.

In certain embodiments, the piezoelectric filter element is a firstpiezoelectric filter element and comprising a second piezoelectricfilter element, wherein the second piezoelectric filter element has atop side and a bottom side opposed to the top side and a left side and aright side opposed to the left side, a top electrode in contact with thetop side, a bottom electrode in contact with the bottom side, a leftacoustic mirror in contact with the left side, and a right acousticmirror in contact with the right side; and wherein the top and bottomelectrodes of the second piezoelectric filter element are electricallyconnected to the active electronic circuit.

In certain embodiments, at least one of the left acoustic mirror andright acoustic mirror comprises a plurality of alternatinghigh-impedance and low-impedance sub-layers.

In another aspect, the disclosed technology includes a transverseacoustic wave filter wafer, comprising: a source wafer comprisingsubstrate material; a patterned sacrificial layer forming sacrificialportions on, over, or in the substrate material, a surface of thesubstrate material, the source wafer, or a surface of the source wafer,the sacrificial portions defining separate anchors between thesacrificial portions; and a transverse bulk acoustic wave filteraccording to claim 1 disposed entirely over each sacrificial portion.

In another aspect, the disclosed technology includes a transverseacoustic wave filter wafer, comprising: a device wafer comprisingsubstrate material; a patterned sacrificial layer forming sacrificialportions on, over, or in the substrate material, a surface of thesubstrate material, the device wafer, or a surface of the device wafer,the sacrificial portions defining separate anchors between thesacrificial portions; a transverse bulk acoustic wave filter disposedentirely over each sacrificial portion, the transverse bulk acousticwave filter comprising a piezoelectric filter element having a top side,a bottom side, a left side, and a right side, wherein the right side isopposed to the left side and the bottom side is opposed to the top side,a top electrode in contact with the top side, a bottom electrode incontact with the bottom side, a left acoustic mirror in contact with theleft side, a right acoustic mirror in contact with the right side, and afractured or separated tether; and an electrical connection electricallyconnected to the top electrode and an electrical connection electricallyconnected to the bottom electrode.

In certain embodiments, the wafer comprises a semiconductor layerdisposed entirely over each sacrificial portion between the sacrificialportion and the transverse bulk acoustic wave filter, the semiconductorlayer comprising an active electronic circuit to which the electricalconnections are electrically connected.

In another aspect, the disclosed technology includes a heterogeneousdevice, the device including: a first substrate comprising a firstmaterial; an active first circuit formed in or on the first substrate,the active first circuit comprising one or more first connection padsconnected to the active first circuit for providing signals to theactive first circuit or receiving signals from the active first circuit;a second substrate separate, distinct, and independent from the firstsubstrate, the second substrate comprising a second material differentfrom the first material, and the second substrate directly or indirectlymicro-transfer printed on the first substrate; two or more electrodes ora second circuit formed in or on the second substrate, the electrodes orsecond circuit comprising one or more second connection pads connectedto the electrodes or second circuits for providing signals to theelectrodes or receiving signals from the electrodes; and one or moreelectrical conductors electrically connecting one or more of the firstconnection pads to one or more of the second connection pads.

In certain embodiments, the device includes a plurality of the electrodepairs or second circuits formed on or in the second substrate whereinthe first connection pads are electrically connected to the secondconnection pads of the plurality of electrode pairs or second circuitswith the one or more electrical conductors.

In certain embodiments, the device includes a plurality of the separate,distinct, and independent second substrates micro-transfer printed onthe first substrate wherein the first connection pads are connected tothe second connection pads with the one or more electrical conductors.

In certain embodiments, the second substrate is micro-transfer printeddirectly or indirectly on the first circuit formed on or in the firstsubstrate.

In certain embodiments, the first circuit is located at least partiallybetween the second substrate and at least portions of the firstsubstrate.

In certain embodiments, the second substrate is adhered to the firstsubstrate with a layer of adhesive.

In certain embodiments, the second substrate includes at least a portionof a tether.

In certain embodiments, the second substrate is crystalline, asemiconductor, a crystalline semiconductor, or a ceramic.

In certain embodiments, the first substrate has a length or breadthdimension of less than or equal to 1 mm, less than or equal to 800 μm,less than or equal to 600 μm, less than or equal to 400 μm, or less thanor equal to 200 μm.

In certain embodiments, the heterogeneous device is a surface mountdevice.

In certain embodiments, the first substrate or the second substrate hasa width from 2 to 5 μm, 5 to 10 μm, 10 to 20 μm, or 20 to 50 μm, thefirst substrate or the second substrate has a length from 2 to 5 μm, 5to 10 μm, 10 to 20 μm, or 20 to 50 μm, or the first substrate or thesecond substrate has a height from 2 to 5 μm, 4 to 10 μm, 10 to 20 μm,or 20 to 50 μm.

In certain embodiments, the second connection pads are electricallyconductive protrusions or spikes extending from the second substrate inelectrical contact with the first connection pads and constitute the oneor more electrical conductors.

In certain embodiments, the heterogeneous device is a surface-mountdevice.

In another aspect, the disclosed technology includes a method of makinga heterogeneous device, the method including: providing a firstsubstrate with an active first circuit formed in or on the firstsubstrate, the first circuit comprising one or more first connectionpads connected to the first circuit for providing signals to the firstcircuit or receiving signals from the first circuit; providing a secondsubstrate separate, distinct, and independent from the first substrate,two or more electrodes or a second circuit formed in or on the secondsubstrate, and two or more second connection pads connected to theelectrodes or second circuit for providing signals to or receivingsignals from the electrodes or second circuit; directly or indirectlymicro-transfer printing the second substrate on the first substrate; andelectrically connecting one or more of the first connection pads to oneor more of the second connection pads.

In certain embodiments, the method includes providing a plurality ofelectrode pairs or second circuits on the second substrate; andelectrically connecting one or more of the second connection pads ofeach of the second circuits to one or more of the first connection pads.

In certain embodiments, the method includes providing a plurality ofsecond substrates; mounting the second substrates on the firstsubstrate; and electrically connecting one or more of the secondconnection pads of each of the second substrates to one or more of thefirst connection pads.

In certain embodiments, the second connection pads are electricallyconductive protrusions or spikes extending from the second substrate,and comprising pressing the electrically conductive protrusions orspikes against or into the first connection pads to form an electricalconnection between the second circuit and the first circuit so that theelectrically conductive protrusions or spikes form the one or moreelectrical conductors.

In certain embodiments, the second substrate is micro-transfer printeddirectly or indirectly onto the first circuit formed on or in the firstsubstrate.

In certain embodiments, the first circuit is located at least partiallybetween the second substrate and at least portions of the firstsubstrate.

In certain embodiments, the second substrate comprises at least aportion of a tether.

In certain embodiments, the first substrate or the second substrate hasa width from 2 to 5 μm, 5 to 10 μm, 10 to 20 μm, or 20 to 50 μm, thefirst substrate or the second substrate has a length from 2 to 5 μm, 5to 10 μm, 10 to 20 μm, or 20 to 50 μm, or the first substrate or thesecond substrate has a height from 2 to 5 μm, 4 to 10 μm, 10 to 20 μm,or 20 to 50 μm.

In certain embodiments, the heterogeneous device is a surface-mountdevice.

In another aspect, the disclosed technology includes a method of makingan acoustic wave filter wafer, the method including: providing a supportwafer and forming an optional buffer layer on the support wafer; forminga piezoelectric material element on the buffer layer or the supportwafer; forming one or more electrodes on the piezoelectric materialelement; optionally forming an acoustic mirror layer on the one or moreelectrodes; providing a semiconductor substrate with an activeelectronic circuit formed in or on the semiconductor substrate, theactive electronic circuit comprising one or more circuit connection padsconnected to the active electronic circuit for providing signals to theactive electronic circuit or receiving signals from the activeelectronic circuit; adhering the semiconductor substrate to the one ormore electrodes or acoustic mirror layer; removing the support wafer andoptionally removing the optional buffer layer; and electricallyconnecting the electrode to the active electronic circuit.

In certain embodiments, the electrode is a first electrode andcomprising forming a second electrode on a side of the piezoelectricmaterial opposite the first electrode and electrically connected thesecond electrode to the active electronic circuit.

In certain embodiments, the method includes forming an acoustic mirroron or over the second electrode.

In certain embodiments, the method includes forming an acoustic mirroron or over the piezoelectric material layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, aspects, features, and advantages ofthe present disclosure will become more apparent and better understoodby referring to the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1A is a schematic plan view of an embodiment of the presentinvention;

FIG. 1B is a cross section of an embodiment of the present inventiontaken across the cross section line A of FIG. 1A;

FIG. 1C is a detail schematic plan view of a piezoelectric substrate andelectrodes according to an embodiment of the present invention;

FIG. 2 is a cross section of another embodiment of the presentinvention;

FIG. 3 is a schematic plan view of a filter substrate and a plurality ofacoustic wave filters with a common piezoelectric layer according toanother embodiment of the present invention;

FIG. 4 is a schematic plan view of a plurality of filter substrates anda plurality of corresponding acoustic wave filters with distinct,separate and independent piezoelectric layers on a support substrateaccording to yet another embodiment of the present invention;

FIG. 5 is a flow diagram illustrating a method of the present invention;

FIG. 6 is another flow diagram illustrating another method of thepresent invention;

FIG. 7 is a cross section of an embodiment of the present inventionhaving an acoustic wave filter with electrically connecting protrusions;

FIG. 8 is a cross section of a surface-mount embodiment of the presentinvention;

FIGS. 9A-9M are sequential cross sections illustrating a method ofmaking a compound acoustic filter wafer and device of the presentinvention;

FIG. 10 is a diagram illustrating the use of a plurality of acousticwave devices in a common circuit according to an embodiment of thepresent invention;

FIGS. 11A-11C are sequential cross sections illustrating a method ofmaking a device of the present invention;

FIG. 12 is a cross section illustrating a compound acoustic filter waferand micro-transfer printable device of the present invention;

FIG. 13 is an upper and lower perspective of the sides of apiezoelectric filter element according to embodiments of the presentinvention;

FIG. 14 is a cross section illustration of a piezoelectric filterelement with left and right acoustic mirrors according to embodiments ofthe present invention;

FIG. 15 is a plan view illustration of a piezoelectric filter elementwith left and right and front and back acoustic mirrors according toembodiments of the present invention;

FIG. 16 is a cross section illustration of a piezoelectric filterelement with left and right and top and bottom acoustic mirrorsaccording to embodiments of the present invention;

FIG. 17 is a cross section illustration of a transverse bulk acousticwave filter and a support substrate with an active electronic circuitaccording to embodiments of the present invention;

FIG. 18 is a cross section illustration of a plurality of transversebulk acoustic wave filters and a support substrate with an activeelectronic circuit according to embodiments of the present invention;

FIG. 19 is a cross section illustration of a wafer comprising atransverse bulk acoustic wave filter disposed over a sacrificial portionaccording to an embodiment of the present invention;

FIG. 20 is a cross section illustration of a wafer comprising asemiconductor layer and a transverse bulk acoustic wave filter disposedover a sacrificial portion according to an embodiment of the presentinvention; and

FIG. 21 shows micrographs of transverse bulk acoustic wave piezoelectricfilter elements on a source wafer, released from a source wafer, andprinted to a destination substrate according to embodiments of thepresent invention.

The features and advantages of the present disclosure will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings, in which like reference charactersidentify corresponding elements throughout. In the drawings, likereference numbers generally indicate identical, functionally similar,and/or structurally similar elements. The figures are not drawn to scalesince the variation in size of various elements in the Figures is toogreat to permit depiction to scale.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the schematic plan view of FIG. 1A, the schematic crosssection of FIG. 1B taken across cross section line A of FIG. 1A, and thedetail schematic plan view of FIG. 1C, in an embodiment of the presentinvention, a compound acoustic wave filter device 10 includes a supportsubstrate 20. In one embodiment, the support substrate is asemiconductor substrate that includes an active electronic circuit 22formed in or on the semiconductor support substrate 20, for example,using photolithographic methods found in the integrated circuitindustry. The active electronic circuit 22 can be, for example, an RFcircuit for filtering, amplifying, or otherwise processing radiofrequency signals. The support substrate 20 or active electronic circuit22 includes two or more circuit connection pads 24 for providing signalsto the active electronic circuit 22 or receiving signals from the activeelectronic circuit 22, if present. An acoustic wave filter 70 includes apiezoelectric filter element 30 and two or more electrodes on thepiezoelectric filter element. The acoustic wave filter 70 ismicro-transfer printed with an adhesive layer 50 between the supportsubstrate 20 and the acoustic wave filter 70.

The adhesive layer can be a layer formed on the support substrate 20 oron the acoustic wave filter 70, or a layer located between the supportsubstrate 20 and the acoustic wave filter 70. The adhesive layer 50 canbe patterned and need not be uniformly present over the supportsubstrate 20. For example, the adhesive layer 50 can be present only inlocations where the acoustic wave filters 30 are intended and can coveronly a portion of the acoustic wave filter area 31. The adhesive layer50 can be coated, provided as a laminate, or inkjet deposited either onthe support substrate 20 or the acoustic wave filter 30. The inkjetdeposition can provide a pattern of drops, for example, drops whoselocation corresponds to the location of the acoustic wave filters 70.The piezoelectric filter element 30 can include a substrate that isseparate, distinct, and independent from the support substrate 20. Thecircuit connection pads 24 can be connected to the active electroniccircuit 22, if present, and the active electronic circuit 22 can, atleast in part, control the acoustic wave filter 70. Additionalconductive elements such as wires can be provided on the supportsubstrate 20, for example electrically connected to the circuitconnection pads 24 forming a circuit, such as a passive circuit, orconnected to the active electronic circuit 22, if present.

The compound acoustic wave filter device 10 is a compound device becauseit incorporates two different structures (e.g., the support substrate 20and the acoustic wave filter 70); in an embodiment, the supportsubstrate 20 and the acoustic wave filter 70 include, incorporate, orare two different materials. The two different materials can havedifferent attributes, can be processed separately, and can bephotolithographic-process incompatible.

Two or more electrodes 32 are formed or disposed in or on thepiezoelectric filter element 30 and are electrically connected to filterconnection pads 34 for providing electrical signals to and from theelectrodes 32. In cooperation with the filter element 30, the electrodes32 can form or are connected to a transducer. Alternatively, referringspecifically to FIG. 1C, in cooperation with the filter element 30 theelectrodes 32 form or are connected to a first transducer 36 forconverting a first electrical signal to an acoustic wave 60 thatpropagates in or on the filter element 30 and a second transducer 38 forconverting the acoustic wave 60 to a second electrical signal differentfrom the first electrical signal. This structure can form a surfaceacoustic wave filter 70.

One or more electrical conductors 40 electrically connect one or more ofthe circuit connection pads 24 to one or more of the electrodes 32through the filter connection pads 34. The active electronic circuit 22or additional conductive elements on the support substrate 20, ifpresent, are thus electrically connected to the electrodes 32. Thesupport substrate 20 can have a process side 26 over which the filterelement 30 is micro-transfer printed. The filter element 30 can have afilter substrate area 31 that is smaller than the support substrate area21 or the active electronic circuit area 23.

The piezoelectric filter element 30 is also referred to herein as afilter element 30, a piezoelectric substrate 30, piezoelectric layer 30,filter substrate 30, a filter layer 30, or second substrate 30. Asdiscussed further below, the piezoelectric filter element 30 can firstbe deposited as a layer on another underlying layer and then, uponremoval of the underlying layer, serve as a substrate for other layers.

The compound acoustic wave filter device 10 of the present invention canhave the two or more electrodes 32 formed on a common side of the filterelement 30 so that the acoustic wave filter 70 is a surface acousticwave filter 70. Alternatively, referring to FIG. 2, the compoundacoustic wave filter device 10 of the present invention can have the twoor more electrodes 32 formed on opposite sides of the filter element 30so that the acoustic wave filter 70 is a bulk acoustic wave filter 70.

As shown in FIGS. 1B and 2, the filter element 30 can be micro-transferprinted on or in combination with the adhesive layer and adhereddirectly to the support substrate 20, layers formed on the supportsubstrate 20, or on the active electronic circuit 22 or additionalconductive elements formed on or in the support substrate 20, ifpresent. In an embodiment, the active electronic circuit 22 oradditional conductive elements are a part of the support substrate 20 orform layers on the support substrate 20. The support substrate 20 caninclude semiconductor material 25 or non-semiconductor material orlayers, for example conductive, patterned conductive layers, dielectriclayers, or patterned dielectric layers. As used herein, micro-transferprinted on or over can include adhered to after a micro-transferprinting operation. A micro-transfer printed acoustic wave filter device70 can include at least a portion of a tether 94 from a source wafer 29on which the acoustic wave filter 70 originates. Portions of a tether 94result from fracturing a tether 94 on a source wafer 29 during themicro-transfer printing process (described with respect to FIG. 9Kbelow). The tethers 94 can be formed from one or more layers of theacoustic wave filter 70 or other layers disposed on the source wafer 29.In embodiments, the active electronic circuit 22 can be located at leastpartially between the acoustic wave filter 70 or the filter element 30and the support substrate 20 (as shown). This arrangement canefficiently use the available area of the support substrate 20.Alternatively, the active electronic circuit 22 can be located to one ormore of the sides of the filter element 30 or acoustic wave filter 70(not shown).

To facilitate securing the filter element 30 to the support substrate20, a layer 50 or pattern of adhesive is provided between the acousticwave filter 70 and the support substrate 20. The adhesive can becurable, for example, responsive to heat or electromagnetic radiation tocure and adhere the acoustic wave filter 70 to the support substrate 20.The adhesive can be a polymer or resin, for example SU8, and can becoated on the support substrate 20 or the acoustic wave filter 70 or thefilter element 30, or provided as a laminate between the supportsubstrate 20 and the acoustic wave filter 70 or filter element 30, orpattern-wise inkjet deposited on the support substrate 20 or theacoustic wave filters 30. In an embodiment, the adhesive layer 50 has anextent or area over the support substrate 20 that is different from theextent or area of the filter element 30 or acoustic wave filter 70. Theextent is taken in a plane parallel to the surface 26 of the supportsubstrate 20 on which the acoustic wave filter 70 or filter element 30is micro-transfer printed. The adhesive can be patterned.

In embodiments of the present invention, the support substrate 20 canhave two relatively flat and substantially parallel opposing sides andcan be any structure having a process side 26 suitable for thedeposition, processing, and patterning of active or passive electronicstructures useful in forming patterned conductors or an activeelectronic circuit 22 and on which the acoustic wave filter 70 or filterelement 30 can be micro-transfer printed. Such structures can includetransistors, diodes, conductors, capacitors, and resistors and includepatterned semiconductor structures, doped semiconductor structures,dielectrics such as silicon oxides and silicon nitrides, and conductorssuch as aluminum, copper, gold, silver, titanium, tantalum, and tin oralloys of such materials. The support substrate 20 can be glass,polymer, plastic, ceramic, semiconductor, or metal and can be rigid orflexible. For example, photolithographic processes for making integratedcircuits or processing substrates can be employed with suitablesemiconductor support substrates 20. The semiconductor supportsubstrates 20 can include semiconductor materials such as silicon orcompound semiconductor materials composed of two or more elements fromdifferent groups of the periodic table such as a III-V or II-VIsemiconductor substrate. In an embodiment, the support substrate 20 is acrystalline semiconductor substrate, such as a crystalline siliconsemiconductor in which circuits, such as CMOS circuits, can be formedusing photolithographic processes. By using crystalline semiconductorsubstrate 30, better performance is achieved than, for example, might befound in a structure using amorphous or polycrystalline semiconductormaterials.

According to embodiments of the present invention, the acoustic wavefilter 70 and filter element 30 are micro-transfer printed onto thesupport substrate 20. As intended herein, to be micro-transfer printedupon means that separate substrates are separately produced and thenbrought into proximity using a transfer stamp and then adhered together.The acoustic wave filter 70 or filter element 30 and the supportsubstrate 20 can be, for example, unpackaged bare die that are directlyadhered together. As also intended herein, the acoustic wave filter 70or filter element 30 micro-transfer printed on the support substrate 20also means that the acoustic wave filter 70 or filter element 30 can bemicro-transfer printed on or over the active electronic circuit 22 oradditional conductive elements on or in the support substrate 20 or alayer on the active electronic circuit 22, for example the adhesivelayer 50. To be micro-transfer printed on or adhered to the activeelectronic circuit 22 means that the acoustic wave filter 70 or filterelement 30 is micro-transfer printed on or adhered to any of theelements of the active electronic circuit 22, for example upon asemiconductor layer, a patterned or doped semiconductor layer orstructure, a conductor layer or patterned conductor, a dielectric layer,a patterned dielectric layer, a protective layer, or any other elementof the active electronic circuit 22.

In contrast, as intended herein a layer formed on a semiconductorsubstrate, for example by evaporation, sputtering, or ion beam exposure,whether patterned or not or annealed or not, is not micro-transferprinted upon or adhered to a support substrate 20 but rather is fused orwelded to the underlying layer. Such a structure does not includeseparate, independent, and distinct substrates, one mounted upon theother and is therefore distinct and different from the micro-transferprinting embodiments of the present invention. As used herein, separate,independent, and distinct substrates are separately constructed,optionally at different times and at different locations using at leastsome different processes and on different wafers. After they areconstructed, the separate, independent, and distinct substrates can betransported and stored separately and independently. Methods of thepresent invention disclose micro-transfer printing one substrate (e.g.,the filter element 30 or acoustic wave filter 70) onto another separate,independent, and distinct substrate (e.g., the support substrate 20) andelectrically interconnecting them with the electrical conductors 40. Thesubstrates remain separate, independent, and distinct after they arecombined into a common structure, since the substrates themselves bothremain present in the combined structure.

The active electronic circuit 22 is a circuit that includes at least oneactive component or element, for example a transistor, a diode, anamplifier, an oscillator, or a switch. Passive components such asconductors, patterned conductors, resistors, capacitors, and inductorscan also be included in the active electronic circuit 22. Elements ofthe active electronic circuit 22 are electrically connected to circuitconnection pads 24. The circuit connection pads 24 are portions of theactive electronic circuit 22 that are also available to make electricalconnections with electrical devices external to the active electroniccircuit 22, for example such as controllers, power supplies, ground, orsignal connections. Similarly, the filter connection pads 34 areportions of the electrodes 32 or electrically conductive areaselectrically connected to the electrodes 32. The circuit connection pads24 or filter connection pads 34 can be, for example, rectangular orcircular areas of electrically conductive materials such as theconductors listed above, accessible or exposed to external elements suchas wires or conductors, including the electrical conductors 40. Thecircuit connection pads 24 or filter connection pads 34 can have anyshape conducive to the formation of electrical connections.

Electrical connections to the circuit connection pads 24 can be madeusing solder and solder methods, photolithographic processes, conductiveink deposition by inkjet, or by contacting and possibly penetrating thecircuit connection pads 24 with electrically conductive protrusions orspikes formed in or on a device with another substrate separate,distinct, and independent from the support substrate 20 and connected toelectrodes 32 in the other substrate (FIG. 7). The other substrate canbe the piezoelectric filter element 30 and the electrically conductiveprotrusions or spikes can be the electrical conductors 40. Electricalconnections between conductors or an active first circuit on a firstsubstrate (e.g., the active electronic circuit 22 on the supportsubstrate 20) and electrodes on a second substrate (e.g., the electrodes32 on the filter element 30) can be made by mechanically pressingconductive protrusions on the second substrate 30 in alignment against,into, onto, or through circuit connection pads 24 on the first substrate20 to form electrical interconnections without photolithographicprocessing and are described in U.S. patent application Ser. No.14/822,864 entitled “Chiplets with Connection Posts” whose contents areincorporated by reference in its entirety. In an embodiment, the filterconnection pads 34 can be the base of the electrically conductiveprotrusions or spikes.

As intended herein, the electrically conductive protrusions or spikespressed into, onto, or through the circuit connection pads 24 areadhered to the circuit connection pads since the friction providedbetween the conductive protrusions or spikes and the circuit connectionpads 24 causes them to adhere and the layer in which the conductiveprotrusions or spikes are pressed into, onto, or through the circuitconnection pads is therefore an adhesive layer. Furthermore, in anotherembodiment, the adhesive layer 50, or a portion or pattern of theadhesive layer 50 can be provided in combination with the conductiveprotrusions or spikes to adhere the support substrate 20 to the acousticwave filter 70, as shown in FIG. 7.

The piezoelectric filter element 30 can be any substrate or layer havingpiezoelectric properties and on or in which electrodes 32 can be formed.For example, the filter element 30 can include one or more of any of asemiconductor, a compound semiconductor, a III-V semiconductor, a II-VIsemiconductor, a ceramic, a synthetic ceramic, GaN, AlGaN, galliumorthophosphate (GaPO₄), Langasite (La₃Ga₅SiO₁₄), lead titanate, bariumtitanate (BaTiO₃), lead zirconate titanate (Pb[Zr_(x)Ti_(1-x)]O₃ 0≦x≦1),potassium niobate (KNbO₃), lithium niobate (LiNbO₃), lithium tantalate(LiTaO₃), sodium tungstate (Na₂WO₃), Ba₂NaNb₅O₅, Pb₂KNb₅O₁₅, zinc oxide(ZnO), Sodium potassium niobate ((K,Na)NbO₃) (NKN), bismuth ferrite(BiFeO₃), Sodium niobate (NaNbO), bismuth titanate (Bi₄Ti₃O₁₂), sodiumbismuth titanate (Na_(0.5)Bi_(0.5)TiO₃), wurtzite, polyvinylidenefluoride, or aluminum nitride (AlN). The filter element 30 can beprocessed using photolithographic methods to form the electrodes 32 andcan have two relatively flat and substantially parallel opposing sides.Alternatively, other methods such as micro-embossing and inkjetdeposition can be used to form structures on the piezoelectric filterelement 30. The piezoelectric filter element 30 can be crystalline. Inan embodiment, the processing materials and methods of the filterelement 30 and electrodes 32 are at least partially different from andincompatible with the processing materials and methods of the supportsubstrate 20 or active electronic circuit 22.

The support substrate 20 and the filter element 30 can take a variety offorms, shapes, sizes, and materials. In one embodiment, the filterelement 30 is thicker than the support substrate 20. In anotherembodiment, the filter element 30 is thinner than the support substrate20, or the filter element 30 and the support substrate 20 can have thesame thickness. The support substrate 20 can have a thickness less than20 microns, less than 10 microns, or less than 5 microns. The filterelement 30 can have a thickness less than 10 microns, less than 5microns, or less than 1 micron. Alternatively, the filter element 30 canhave a thickness greater than 0.5 microns, greater than 1 micron,greater than 2 microns, or greater than 5 microns. Such a variety ofsizes can enable highly integrated and small structures useful in acorresponding variety of electronic systems.

Referring again to FIG. 2, in an embodiment of the present invention,the electrodes 32 form transducers 36 in cooperation with the filterelement 30. The filter connection pads 34 are available to makeelectrical connections with electrical devices external to the filterelement 30, for example signal connections to the active electroniccircuit 22. Electrical connections to the filter connection pads 34 canbe made using solder and soldering methods or photolithographicprocesses. Alternatively, the filter connection pads 34 can beelectrically connected to electrically conductive protrusions or spikesthat extend from the filter element 30 to form the electrical conductors40 and can be pressed against the circuit connection pads 24 on thesupport substrate 20 to form an electrical connection between theelectrodes 32 and the circuit connection pads 24, as described above andillustrated in FIG. 7.

As shown in FIG. 1C, the electrodes 32 can be patterned and arranged ona common side of the filter element 30 to form capacitors havinginterdigitated projections or fingers that, upon the application of adynamic voltage differential across the terminals of the capacitor,forms a corresponding dynamic electrical field that causes a surfaceacoustic wave 60 to form in the piezoelectric filter element 30 or thatresponds to the surface acoustic wave 60 in the piezoelectric filterelement 30 and forms a voltage differential across the terminals of thecapacitor. Alternatively, as shown in FIG. 2, the electrodes 32 formconductive areas on opposite sides of the filter element 30 defining acapacitor. Upon the application of a dynamic voltage differential acrossthe terminals of the capacitor, a corresponding dynamic electrical fieldis formed in the filter element 30 that causes a bulk acoustic wave 60to form in the piezoelectric filter element 30. Thus, the electrodes 32are patterned or disposed to form an electrical or magnetic field whenan electrical potential is applied to the electrodes 32. The electrodes32 can comprise one or more capacitors and, in cooperation with thefilter element 30, comprise one or more transducers (e.g., a singletransducer in FIG. 2 and first and second transducers 36, 38 in FIG.1C).

A transducer converts energy in one form to energy in another form. Forexample, the first transducer 36 converts electrical energy (anelectrical current in the electrodes 32) into an electrical field acrossthe interdigitated fingers of the capacitor or through the filterelement 30 and then into surface or bulk acoustic waves 60 in thepiezoelectric filter element 30. In the embodiment of FIG. 1C, thesecond transducer 38 does the reverse by converting an acoustic wave (amechanical vibration for example in a crystal lattice) into anelectrical field across the interdigitated fingers of a capacitor thatinduces an electrical current in the electrodes 32.

As used herein, an acoustic mirror is a passive device comprising one ormore sublayers that reflect sound waves of one or more desiredfrequencies or ranges of frequencies. The different sub-layers of anacoustic mirror can transmit sound waves at different velocities,enabling constructive and destructive interference of the sound waves atfrequencies depending on the relative thicknesses and sound velocitiesof the materials within the one or more sub-layers. Referring again toFIG. 2, in an embodiment of the present invention, an acoustic mirrorlayer 35 is located at least partially on a side of one of theelectrodes 32 opposite the filter element 30 with the filter element 30between the support substrate 20 and the acoustic mirror layer 35.Alternatively, an acoustic mirror layer 35 is located on a side of oneof the electrodes 32 opposite the filter element 30 with the acousticmirror layer 35 between the support substrate 20 and the filter element30. In another embodiment, an acoustic mirror layer 35 is disposed inboth locations. In a further embodiment discussed further below withrespect to FIG. 9L, at least one of the acoustic mirror layers 35 ischemically etch-resistant or at least one of the electrodes 32 ischemically etch resistant.

Referring to FIG. 3, in an embodiment of the present invention, theelectrodes 32 form a plurality of electrode pairs. Each electrode pairforms a separate transducer 36 formed on or in the filter element 30,corresponding to the embodiment of FIG. 1C. Pairs of transducers 36, 38form individual surface acoustic wave filters 70A, 70B, 70C on a commonfilter element 30. Each of the electrodes 32 is connected to a circuitand a filter connection pad 24, 34 and to the active electronic circuit22 with the electrical conductors 40. Thus, multiple acoustic wavefilters 70A, 70B, 70C can be provided in a common filter element 30 andelectrically connected to a common active electronic circuit 22 toprovide multiple filtering operations. Multiple acoustic wave filters 70electrically connected to a common set of conductors on the supportsubstrate 20 or to a common active electronic circuit 22 can improve theintegration density of the compound acoustic wave filter device 10 ofthe present invention.

In another embodiment of the present invention illustrated in FIG. 4, aplurality of acoustic wave filters 70A, 70B, 70C, 70D each having aseparate, distinct, and independent piezoelectric filter element 30(filter element 30A, filter element 30B, filter element 30C, and filterelement 30D) and two or more electrodes 32, is micro-transfer printedonto or over the support substrate 20. The plurality of filter elements30 can have reduced acoustic wave cross talk and improved performancecompared to the embodiment of FIG. 3. The electrodes 32 of each of thefilter elements 30A, 30B, 30C, 30D are connected to correspondingcircuit connection pads 24 and filter connection pads 34 with one ormore of the electrical conductors 40. Although the acoustic wave filters70A, 70B, 70C, 70D are illustrated in FIG. 4 as surface acoustic wavefilters 70A, 70B, 70C, 70D corresponding to FIG. 1C, in anotherembodiment the acoustic wave filters 70A, 70B, 70C, 70D are bulkacoustic wave filters 70A, 70B, 70C, 70D, each corresponding to the bulkacoustic wave filter 70 of FIG. 2.

In an embodiment of the present invention, all of the acoustic wavefilters 70A, 70B, 70C, 70D are substantially identical. In anotherembodiment, some of the acoustic wave filters 70 are different fromothers. For example, a first acoustic wave filter 70A of the pluralityof acoustic wave filters 70 has one or more first attributes, a secondacoustic wave filter 70B of the plurality of acoustic wave filters 70has one or more second attributes and at least one of the firstattributes is different from at least one of the second attributes.Attributes can include filter element material, crystal latticestructure, impedance at a pre-determined frequency, or size, such asthickness, length, or width. Attributes can also include placement ofelectrodes, electrode material, electrode material composition orstructure, or electrode size, such as thickness, length, or width. Forexample, in one embodiment a first acoustic wave filter 70A can have alow impedance at a desired frequency and a second acoustic wave filter70A can have a high impedance at the desired frequency.

In an embodiment of the present invention, the different acoustic wavefilters 70 are formed on a common acoustic wave filter source wafer 12,for example using photolithographic processes, or from a plurality ofsubstantially identical acoustic wave filter source wafers 12. Inanother embodiment, multiple, different acoustic wave filter sourcewafers 12 are provided having different acoustic wave filters 70 onthem. For example, a first acoustic wave filter wafer 12 has firstacoustic wave filters 70A, a second acoustic wave filter wafer 12 hassecond acoustic wave filters 70B, and both the first and second acousticwave filters 70A, 70B from the respective first and second acoustic wavefilter wafers 12 are micro-transfer printed onto the adhesive layer 50.The acoustic wave filter source wafers 12 can be different and theacoustic wave filters 70 from the different acoustic wave filter sourcewafers 12 can be different, for example having different materials,crystal lattice structures, sizes, or electrodes. By using differentacoustic wave filter source wafers 12, the task of tuning the filterelements 30 is greatly simplified, since the filter elements 30 can bemade separately using different materials or structures andindependently optimized for their desired characteristics.

Referring to FIG. 10, a network of acoustic wave filters 70A, 70B, 70C,70D are electrically connected to form an RF filter useful fortelecommunications applications. The acoustic wave filters 70A, 70B,70C, 70D of FIG. 10 can correspond to the acoustic wave filters 70A,70B, 70C, 70D of FIG. 4. The acoustic wave filters 70A, 70B, 70C, 70Dcan be different acoustic wave filters 70 from different source wafers12 can have different attributes. Thus, in an embodiment of the presentinvention, the filter structure illustrated in FIG. 10 can beconstructed on a common support substrate 20 and electrically connectedto a common set of conductors on the support substrate 20 or to a commonactive electronic circuit 22. Such an integrated compound acoustic wavefilter device 10 can be very small, for example having a length orbreadth dimension of less than or equal to 1 mm, less than or equal to800 μm, less than or equal to 600 μm, less than or equal to 400 μm, lessthan or equal to 200 μm, less than or equal to 100 μm, less than orequal to 50 μm, or less than or equal to 20 μm. The height of thecompound acoustic wave filter device 10 can be less than or equal to 100μm, less than or equal to 50 μm, less than or equal to 20 μm, less thanor equal to 10 μm, less than or equal to 5 μm, or less than or equal to2 μm. The support substrate 20 likewise can have a length or breadthdimension of less than or equal to 1 mm, less than or equal to 800 μm,less than or equal to 600 μm, less than or equal to 400 μm, less than orequal to 200 μm, less than or equal to 100 μm, less than or equal to 50μm, or less than or equal to 20 μm. The compound acoustic wave filterdevice 10 can be a surface-mount device.

In an embodiment of the present invention the support substrate 20 orthe filter element 30, or both, are chiplets. Chiplets can be smallintegrated circuits or processed substrates, for example bare die, thatare integrated into a compound device structure using micro-transferprinting. In an embodiment, the acoustic wave filter 70 or filterelement 30 is not an integrated circuit with active circuit componentsbut rather a small substrate processed using photolithographic methodsto provide passive elements such as electrodes 32 and filter connectionpads 34 thereon. Alternatively, the filter element 30 is an integratedcircuit with active circuit components. The compound acoustic wavefilter device 10 can be subsequently packaged after integrating thesupport substrate 20 with the acoustic wave filter 70 usingmicro-transfer printing. In various embodiments, the support substrate20, acoustic wave filter 70, or the filter element 30 has a width from 2to 5 μm, 5 to 10 μm, 10 to 20 μm, or 20 to 50 μm, the support substrate20 acoustic wave filter 70, or the filter element 30 has a length from 2to 5 μm, 5 to 10 μm, 10 to 20 μm, or 20 to 50 μm, or the supportsubstrate 20 acoustic wave filter 70, or the filter element 30 has aheight from 2 to 5 μm, 4 to 10 μm, 10 to 20 μm, or 20 to 50 μm. Suchsmall substrate elements provide a high degree of integration andconsequently reduced manufacturing costs and improved performance.

Referring to FIG. 5, a method of making a compound acoustic wave filterdevice 10 includes providing a support substrate 20. In the FIG. 5illustration, the support substrate 20 is a semiconductor substrate withactive electronic components. In another embodiment (FIG. 8), thesupport substrate 20 is a passive substrate, for example including onlyelectrical conductors and connection pads (not shown in FIG. 8). Thesemiconductor substrate 20 has an active electronic circuit 22 formed inor on the support substrate 20 in step 105. Alternatively, the supportsubstrate 20 can first be provided in step 100 and the active electroniccircuit 22 formed in or on the support substrate 20 in step 110. Theactive electronic circuit 22 includes one or more circuit connectionpads 24 connected to the active electronic circuit 22 for providingsignals to the active electronic circuit 22 or receiving signals fromthe active electronic circuit 22. A piezoelectric filter element 30separate, distinct, and independent from the support substrate 20 isprovided in step 120 and electrodes 32 formed in or on the filterelement 30 in step 130 to form an acoustic wave filter 70. The acousticwave filter 70 includes one or more transducers 36 for converting anelectrical signal to an acoustic wave 60 in or on the filter element 30.Alternatively, a first transducer 36 converts a first electrical signalto an acoustic wave 60 in or on the filter element 30 and a secondtransducer 38 converts the acoustic wave 60 to a second electricalsignal different from the first electrical signal. In anotherembodiment, the filter element 30 and electrodes 32 are provided in asingle step 125. In one embodiment of the present invention, step 130provides a plurality of acoustic wave filters 70 on a single filterelement 30 (e.g., corresponding to the structure of FIG. 3), for exampleby providing four or more electrodes 32 on the filter element 30 formingtwo or more acoustic wave filters 70. Alternatively or in addition, step125 is repeated to provide a plurality of acoustic wave filters 70 onseparate filter elements 30 (e.g., corresponding to the structure ofFIG. 4).

A layer 50 of adhesive is disposed between the filter element 30 and thesupport substrate 20 in step 140, for example on the filter element 30or acoustic save filter 70, on the support substrate 20, or with alaminate located between the filter element 30 and the support substrate20. The adhesive can be a patterned layer 50 of adhesive, for exampleinkjet-deposited adhesive material, provided by coating, or patternedusing photolithography. The filter element(s) 30 or acoustic wavefilter(s) 70 are mounted on the support substrate 20 in step 150 bymicro-transfer printing. In an alternative embodiment, step 150 isrepeated to provide a plurality of filter elements 30 or acoustic wavefilter(s) 70 micro-transfer printed on the support substrate 20 (e.g.,corresponding to the structure of FIG. 4). The adhesive can be a curableadhesive and in step 160 the adhesive layer 50 is cured to adhere theacoustic wave filter 70 or filter element 30 to the support substrate20. One or more electrodes 32 are connected to the circuit connectionpads 24 or the active electronic circuit 22 or additional conductiveelements on the support substrate 20 (if present) through the filterconnection pads 34, electrical conductors 40, and circuit connectionpads 24 for providing the first electrical signal to the firsttransducer 36 and for receiving the second electrical signal from thesecond transducer 38 (if present) in step 170 to construct a compoundacoustic wave filter device 10 of the present invention. This step canbe provided using photolithographic deposition and patterning ofconductive materials or patterned deposition of conductive materials.Alternatively, the step 170 of connecting the circuit connection pads 34(or active electronic circuit 22, if present) to the filter connectionpads 34 and electrodes 32 can be performed in a common step with themicro-transfer step 140 using the conductive protrusions or spikesillustrated in FIG. 7 and described above so that no separate step 170is necessary.

The integrated assembly can be a surface-mount device. In optional step180, the integrated compound acoustic wave filter device 10 is itselfmicro-transfer printed to a system substrate (for example, a printedcircuit board, glass, or polymer substrate) as part of a compoundmicro-assembly structure and process. Alternatively, other methods suchas pick-and-place can be used, or surface-mount techniques can be usedto dispose the integrated compound acoustic wave filter device 10 to adesired location, for example as part of a larger RF circuit orsubstrate.

In a further embodiment of the present invention, electrical conductors40 are electrically conductive protrusions or spikes extending from thefilter element 30 or acoustic wave filter 70 and the step 150 ofmicro-transfer printing the filter element 30 or acoustic wave filter 70onto the support substrate 20 includes pressing the electricallyconductive protrusions or spikes against, onto, into, or through thecircuit connection pads 24 to form an electrical connection between theelectrodes 32 and the circuit connection pads 24, as also illustrated inFIG. 7. As noted above, an adhesive layer 50 or patterned adhesive layer50 can be used in combination with the conductive protrusions or spikesto provide electrical connections and adhesion between the acoustic wavefilter 30 and support substrate 20.

Referring to FIG. 6, to FIGS. 9A-9M, and to FIG. 2, in anotherembodiment of the present invention, a method of making a compoundacoustic wave filter device 10 includes providing a support wafer 39 instep 200 and as shown in FIG. 9A. The support wafer 39 provides asupport substrate and can be a glass wafer, a dielectric, a metal wafer,a semiconductor wafer, a polymer wafer, a combination of these, or anywafer, sheet, substrate, or structure with a flat surface suitable formaterial deposition or photolithographic processing. Referring to FIG.9B, an optional buffer layer 90 is deposited on the support wafer 39 inoptional step 205. The optional buffer layer 90 includes a materialselected to enable subsequent removal of the support wafer 39 and toprovide a surface on which a piezoelectric layer 30 forming a filterelement 30 can be formed. The buffer layer can be a piezo materialnucleation layer that reduces lattice mismatch between the support wafer39 and the filter element 30, and can include, for example, siliconnitride or aluminum nitride deposited by vapor deposition. Since thefilter element 30 can be crystalline, lattice mismatch between thefilter element 30 and the support wafer 39 can increase defects withinthe filter element 30 and reduce the performance of the acoustic wavefilter 70.

In step 210 illustrated in FIG. 9C, the piezoelectric layer 30 isformed, for example by vapor deposition or other material depositionmethods (e.g. chemical vapor deposition, sputtering, or atomic layerdeposition) and, in an embodiment, forms a crystalline layer. Suitablepiezoelectric filter layer 30 materials are listed above.

Referring next to FIG. 9D and step 220 of FIG. 6, an electrode 32 isformed on the piezoelectric layer 30 and can be patterned, if desired,using photolithographic processes, for example to form the capacitivestructures illustrated in FIG. 1C. The electrodes 32 can be a metal, forexample tantalum, molybdenum, platinum, titanium, gold, silver,aluminum, tungsten, combinations of such metals, or metal oxides, forexample indium tin oxide or aluminum zinc oxide.

Referring next to FIG. 9E and optional step 225 of FIG. 6, an optionalacoustic mirror layer 35 is formed on the electrode 32 and optionally onthe piezoelectric layer 30 and can be patterned, if desired, usingphotolithographic processes. In an embodiment, a portion of theelectrode 32 is not covered by the optional acoustic mirror layer 35(not shown in FIG. 9E). An acoustic mirror layer 35 can includesub-layers, for example alternating layers of low-impedance (e.g.,dielectric) and high-impedance (e.g., metal) reflector layers (forexample quarter-wave thickness) chosen to constructively anddestructively interfere with the acoustic waves generated in the filterlayer 30 and thereby improve the performance of the acoustic wave filter70.

In step 230 of FIG. 6 and referring to FIG. 9F, a sacrificial layer 28is patterned over the optional acoustic mirror layer 35 and electrode 32to form sacrificial portions (as labeled 28). The patterned sacrificiallayer 28 can be etched to remove the material of the sacrificialportions 28 to form a gap between the acoustic wave filter 70 and thesupport substrate 20. The patterned sacrificial layer 28 can be apatterned layer of etchable material, for example an oxide such assilicon dioxide. FIG. 9G illustrates disposing an adhesive layer 54 onthe patterned sacrificial layer 28 in step 240.

Referring next to step 202 of FIG. 6, a source wafer 29 (also referredto as a handle wafer in this process) is provided. The source/handlewafer 29 can be glass, polymer, metal, or a semiconductor wafer,substrate, sheet, or structure with a flat surface. As shown in FIG. 9H,in step 250 the source/handle wafer 29 is adhered to the adhesive layer54 and, in step 260 the support wafer 39 and optionally the optionalbuffer layer 90 are removed, for example by grinding or by chemicallyetching the optional buffer layer 90 to detach the support wafer 39. Asshown in FIG. 9I, the structure can be turned over or otherwise arrangedto provide a process surface on the filter layer 30.

For clarity, FIG. 9J and the subsequent FIGS. 9J-9M have a largerhorizontal scale. Referring to FIG. 9J, a second electrode 32 isoptionally formed and patterned on the filter element 30 in step 270 andan optional second acoustic mirror layer 35 formed over the electrode 32in step 275 to form a bulk acoustic wave filter 70. The filter element30 is processed to expose the patterned sacrificial layer 28, optionaldielectric insulators 52 are patterned to insulate the filter element30, if necessary, and filter connection pads 34 are formed (FIG. 9K). Inalternative embodiments, the filter connection pads 34 are formed beforeor after the electrodes 32 are formed, the second acoustic mirrors 35are formed, or the filter layer 30 is processed or patterned.

Thus, in an embodiment of the present invention, an acoustic wave filterwafer 12 includes a source wafer 29 of substrate material having apatterned sacrificial layer 28 forming sacrificial portions 28 on, over,or in the substrate material, a surface of the substrate material, thesource wafer 29, or a surface of the source wafer 29. The sacrificialportions 28 define separate anchors 92 between the sacrificial portions28. A piezoelectric acoustic wave filter 70 is formed entirely over eachsacrificial portion 28. The acoustic wave filter 70 includes at least(i) a layer 30 of piezoelectric material and (ii) two or more electrodes32 in or on the piezoelectric material layer 30. The portion of eachacoustic wave filter 70 in contact with the sacrificial portion 28 ischemically and selectively etch-resistant so that the contact portionhas a chemical selectivity different from the patterned sacrificiallayer 28. The contact portion can be a portion of the piezoelectricfilter layer 30 or all of or a portion of an electrode 32. In anembodiment in which one or more acoustic mirror layers 35 are present,the contact portion can be all of or a portion of an acoustic mirrorlayer 35. Because the contact portion has a chemical selectivitydifferent from the patterned sacrificial layer 28, the sacrificialportions 28 can be etched without undue damage to whatever portion ofthe acoustic wave filter 70 is in contact with the sacrificial portions28, for example any or all of the piezoelectric filter layer 30, theelectrode 32, or the acoustic mirror layer 35.

By etching the patterned sacrificial layer 28 in step 280, a tether 94is formed physically connecting the anchor 92 and the acoustic wavefilter 70. Thus, the piezoelectric acoustic wave filter 70 is attachedto the anchor 92 with at least one tether 94. The sacrificial portions28 then form a gap between the acoustic wave filter 70 and thesource/handle wafer 29 so that the acoustic wave filter 70 can bemicro-transfer printed in step 150 onto adhesive layer 50 disposed on orover the support substrate 20 as described with respect to FIG. 5 and asillustrated in FIG. 9L. The adhesive layer 50 is then cured (step 160)and patterned (FIG. 9M), so that the electrical conductors 40 can beformed (step 170) electrically connecting the active electronic circuit22 to the electrode 32 (FIG. 2) to form the compound acoustic wavefilter device 10 of the present invention. Those knowledgeable in thephotolithographic arts will recognize that various elements and layerscan be formed or processed at different times or in different ordersthan as described in the example of FIGS. 9A-9M. The compound acousticwave filter device 10 can be a surface-mount device and be disposed in acircuit on another substrate such as in an RF circuit on a printedcircuit board. Alternatively, the support substrate 20 can itself have asacrificial layer formed, for example under the active electroniccircuit 22 if present, that can be etched to provide a micro-transferprintable compound acoustic wave filter device 10, as described belowwith respect to FIG. 12.

In another embodiment of the present invention and in reference to FIG.8, the acoustic wave filter 70 is micro-transfer printed onto a passivesupport substrate 20. The electrical conductors 40 are formed and adielectric layer 52 is patterned and expose circuit connection pads 24to provide a surface-mount device 78 that can be surface mounted andelectrically connected in a circuit. The support substrate 20 can be apassive substrate that includes conductive wires or circuit connectionpads 24 but does not include active electronic elements such astransistors or diodes.

Referring to FIGS. 11A-11C, in another method of the present invention,the sacrificial layer 28 is not formed (FIG. 9F, step 230). Instead, thesupport substrate 20, active electronic circuit 22, and circuitconnection pads 24 are adhered to the adhesive layer 54 instead of thesource/handle wafer 29 (step 250) as shown in FIG. 11A and the supportwafer 39 and optional buffer layer 90 are removed (FIG. 11B). In thisembodiment, the second electrodes 32 and optional second mirror layer 35are formed and patterned directly over the support substrate 20 (FIG.11C), and the process then continues as described with reference toFIGS. 9L and 9M. This avoids the etching process for the individualacoustic wave filters 70. This approach is particularly useful if thecompound acoustic wave filter device 10 itself is a micro-transferprintable device. In this case, referring to FIG. 12, a sacrificiallayer 28 is provided in the support substrate 20 under the activeelectronic circuit 22 or additional conductive elements, if present andas shown, and etched to form a micro-transfer printable compoundacoustic wave filter device 10 using compound micro-assembly methods.

Referring to FIG. 13, a filter element 30 in a piezoelectric bulkacoustic wave filter can have a rectangular cross section in each ofthree dimensions and can have six sides, a top side 30T and an opposingbottom side 30M, a front side 30F and an opposing back side 30K, and aleft side 30L and an opposing right side 30R. The top and bottom sides30T, 30M are on opposite sides of the filter element 30, the front andback sides 30F, 30K are on opposite sides of the filter element 30, andthe left and right sides 30L, 30R are on opposite sides of the filterelement 30, for example as on opposite sides of a cube. Adjacent sidescan be, but are not necessarily, orthogonal and opposing sides can be,but are not necessarily, parallel. The length of the filter element 30is designated as L, the width is designated as W, and the height (depth,thickness) as H. It will be readily appreciated that the designationstop, bottom, left, right, front, and back, as well as length, width, andheight are arbitrary and can be reversed or exchanged or alternativedescriptors used for the different opposing sides or dimensions of thefilter element 30. In FIG. 13, the upper graphic is a perspective viewof the filter element 30 from above (showing the top side 30T and rightside 30R) and the lower graphic is a perspective view of the filterelement 30 from below (showing the bottom side 30M and left side 30L).

Each filter element 30 can comprise a tether 94 or have a tether 94attached to the filter element 30. The tether 94 can be a fractured orbroken tether 94. In other embodiments (not shown), the tether 94 is aseparated, disengaged, or decoupled tether, for example located on oradjacent to a bottom side 30M of the filter element 30 or a layer formedon the filter element bottom side 30M.

As shown in the illustrations of FIGS. 1-4, 7-9, and 11-12, in certainembodiments, the electrodes 32 are disposed on the top side 30T andbottom side 30M of the filter element 30. The acoustic mirror layers 35are disposed on the electrodes 32 and the top and bottom sides 30T, 30Melectrodes 32. When at least a portion of the electrodes 32 are betweenat least a portion of the acoustic mirror layers 35 and the top andbottom sides 30T, 30M of the filter element 30, they are considered tobe on or adjacent to the top and bottom sides 30T, 30M of the filterelement 30. As discussed above, in some embodiments, the thickness ofthe filter element 30 between the electrodes 30 is pre-determined tocause the acoustic waves 60 formed by providing a voltage across theelectrodes 32 on the filter element 30 to constructively interfere at adesired wavelength in a direction orthogonal to the top and bottom sides30T, 30M of the filter element 30 between the electrodes 32 to form aresonant acoustic wave. Moreover, the acoustic waves 60 in the filterelement 30 cause the filter element 30 to expand and contract not onlyin the dimension between the electrodes 32, but also in the dimensionfrom front to back between the front and back sides 30F, 30K,respectively, and from left to right between the left and right sides30L, 30R, respectively.

In some filter applications that require a very thin filter element 30(a very small H, for example less than or equal to a micron, less thanto two, three, or five microns, less than or equal to ten microns, orless than or equal to twenty microns), it can be difficult to make asuitable filter element 30 with acoustic mirrors layer 35 on the top andbottom sides 30T, 30M of the necessary size that is properly andreliably tuned to the desired wavelength since, with such smallthickness sizes, minor changes in size can result in large changes inresonant frequencies. Therefore, in alternative embodiments, referringto FIG. 14, left and right acoustic mirrors 35L and 35R are provided onthe left side 30L and the right side 30R of the filter element 30,respectively, to provide a transverse bulk acoustic wave filter 71. Thesize of the filter element 30 L from left to right can be chosen toenable constructive interference of resonant transverse acoustic waves62 at a desired wavelength. By providing a filter element 30 thatemploys constructive interference for resonant transverse acoustic waves62, the desired response of the filter element 30 is more readilyachieved while also providing a desired filter element 30 thickness H.

A transverse acoustic wave 62 is an acoustic wave that travels betweenthe left and right sides 30L, 30R of the filter element 30, or betweenthe front and back sides 30F, 30K of the filter element 30. Thus, insome embodiments, a transverse bulk acoustic wave filter 71 comprises apiezoelectric filter element 30 having a top side 30T and a bottom side30M opposed to the top side 30T and a left side 30L and a right side 30Ropposed to the left side 30L. A top electrode 32T is in contact with thetop side 30T of the filter element 30 and a bottom electrode 32B is incontact with the bottom side 30M of the filter element 30. The top andbottom electrodes 32T, 32B are collectively referred to as electrodes32. A left acoustic mirror 35L is in contact with the left side 30L ofthe filter element 30 and a right acoustic mirror 35R is in contact withthe right side 30R of the filter element 30.

In some embodiments of the present invention, the acoustic waves in thepiezoelectric element 30 experience constructive interference in thetransverse direction between the left and right acoustic mirrors 35L,35R but the sizes and structures of the piezoelectric filter element 30between the front and back sides 30F, 30K and the sizes and structuresof the piezoelectric filter element 30 between the top and bottom sides30T, 30M are chosen to provide destructive acoustic wave interferencebetween the respective sides.

In some embodiments of the present invention, additional acousticmirrors are provided on other sides of the piezoelectric element 30. Forexample, referring to FIG. 15, in the case wherein the piezoelectricfilter element 30 has a front side 30F and a back side 30K, a frontacoustic mirror 35F is in contact with the front side 30F and a backacoustic mirror 35K is in contact with the back side 30K. In theseembodiments, the constructive interference of resonant transverseacoustic waves 62 between the left and right acoustic mirrors 35L, 35Ris complemented by constructive interference of resonant transverseacoustic waves 62 between the front acoustic mirror 35F and the backacoustic mirror 35K.

In some embodiments, referring to FIG. 16, the piezoelectric filterelement 30 includes a top acoustic mirror 35T and a bottom acousticmirror 35M. FIG. 2 also illustrates left and right side structures madeof a patterned dielectric layer 52 that can form left and right acousticmirrors 35L, 35R and acoustic mirror layers 35 that can form top andbottom acoustic mirrors 35T, 35M. Because of the top and bottomelectrodes 32, the top and bottom acoustic mirrors 35T, 35M can be onlypartially in direct contact with the piezoelectric filter element 30. Insuch embodiments, the top and bottom electrodes 32 can be or form a partof the top and bottom acoustic mirrors 35T, 35M, respectively. In theseembodiments, the constructive interference of transverse acoustic waves62 between the left and right acoustic mirrors 35L, 35R is complementedby constructive interference of transverse acoustic waves 62 between thefront acoustic mirror 35F and the back acoustic mirror 35K.

In some embodiments, both top and bottom acoustic mirrors 35T, 35M andboth front and back acoustic mirrors 35F, 35K complement the left andright acoustic mirrors 35L, 35R and provide constructive interference inthree dimensions simultaneously for desired acoustic wave frequencies.

The transverse acoustic mirror layers (e.g., left and right acousticmirrors 35L, 35R and front and back acoustic mirrors 35F, 35K) as wellas the acoustic mirror layers 35T, 35M can include sub-layers, forexample alternating layers of low-impedance (e.g., dielectric) andhigh-impedance (e.g., metal) reflector layers (for example quarter-wavethickness) chosen to constructively and destructively interfere with theacoustic waves generated in the filter element 30 by voltage differencesprovided across the electrodes 32.

In certain embodiments, using transverse acoustic waves 62 providesadvantages, such as a reduced thickness, over other bulk acoustic wavefilters using only acoustic waves 60 that experience constructiveinterference through the thickness of the piezoelectric filter elements30. In such embodiments, and referring again to FIG. 13, thepiezoelectric filter element 30 can have a rectangular cross sectiontaken from the left to right sides 30L, 30R. Thus, in some embodimentsof the present invention, the distance between the top side 30T and thebottom side 30M is less than the distance between the left side and theright side 30L, 30R, or is less than or equal to one half, one quarter,one tenth, one twentieth, one fiftieth, 1/100, or 1/200 of the distancebetween the left side 30L and the right side 30R.

In some embodiments in which the piezoelectric filter element 30 has arectangular cross section taken from the front to back sides 30F, 30K,the distance between the top side 30T and the bottom side 30M is lessthan the distance between the front side and the back side 30F, 30K oris less than or equal to one half, one quarter, one tenth, onetwentieth, one fiftieth, 1/100, or 1/200 of the distance between thefront side and the back side 30F, 30K.

In some embodiments, the filter element 30 has a rectangular crosssection taken from the top to the bottom side 30T, 30M (corresponding toa plan view such as FIG. 15). In such embodiments, the distance betweenthe front side and the back side 30F, 30K is less than the distancebetween the left side 30L and the right side 30R or is less than orequal to one half, one third, one quarter, one tenth, or one twentiethof the distance between the left side 30L and the right side 30R.

Thus, piezoelectric filter elements 30 of the present invention can bethin and have an aspect ratio in which the length from left to right isconsiderably greater (e.g., more than two, three, four, five, ten, ortwenty to one) than the width from front to back.

Referring to FIG. 17, in embodiments, the transverse bulk acoustic wavefilter 71 comprises a top electrical conductor 40 in electrical contactwith the top electrode 32T, for example through an optional filterconnection pad 34, and a bottom electrical conductor 40 in contact withthe bottom electrode 32B, for example through another optional filterconnection pad 34. The top electrical conductor 40 can be, but is notnecessarily, disposed at least partially on, in, or as part of the leftacoustic mirror 35L and the bottom electrical conductor 40 can be, butis not necessarily, disposed at least partially on, in, or as part ofthe right acoustic mirror 35R. In some embodiments, the top electricalconductor 40 is insulated from the left side 30L by a dielectricstructure 52 that forms at least a portion of the left acoustic mirror35L and the bottom electrical conductor 40 is insulated from the rightacoustic mirror 35R by a dielectric structure 52 that forms at least aportion of the right acoustic mirror 35R. As shown in FIG. 17, thedielectric structures 52 can include multiple layers of insulatingmaterials whose materials and thickness can be chosen to provide anacoustic mirror having the desired properties of reflection at desiredacoustic frequencies.

As is further shown in FIG. 17, in some embodiments, a transverse bulkacoustic wave filter 71 comprises a support substrate 20 and top andbottom circuit connection pads 24. The piezoelectric filter element 30is adhered to the support substrate 20. For example, and as shown inFIG. 17, the piezoelectric filter element 30 can be adhered by adheringthe bottom electrode 32B to the support substrate 20 with an adhesivelayer 50. The top circuit connection pad 24 is electrically connected tothe top electrode 32T and the bottom circuit connection pad 24 iselectrically connected to the bottom electrode 32, for example throughvias in the adhesive layer 50. The top electrode 32T is on the top side30T of the piezoelectric filter element 30 opposite the supportsubstrate 20 and the bottom electrode 32B is on the bottom side 30M ofthe piezoelectric filter element 30 adjacent to the support substrate20. Thus, electrical access to the electrodes 32 of the transverse bulkacoustic wave filter 71 is available through or on the support substrate20. In some embodiments, the support substrate 20 is a semiconductorsubstrate 20 and the transverse bulk acoustic wave filter 71 furthercomprises an active electronic circuit 22 formed in or on thesemiconductor substrate 20. The active electronic circuit 22 is showedas formed in the semiconductor substrate 20 in FIG. 17. The activeelectronic circuit 22 is electrically connected to the top and bottomcircuit connection pads 24 and thence to the electrodes 32. The activeelectronic circuit 22 can be disposed at least partially between thepiezoelectric filter element 30 and the support substrate 20, as shownin FIG. 17.

Referring to FIG. 18, in some embodiments of the transverse bulkacoustic wave filter 71, the piezoelectric filter element 30 comprises afirst piezoelectric filter element 30A and a second piezoelectric filterelement 30B similar to the first piezoelectric filter element 30A. Thetop and bottom electrodes 32T, 32B of the first piezoelectric filterelement 30A and the top and bottom electrodes 32T, 32B of the secondpiezoelectric filter element 30B are electrically connected to theactive electronic circuit 22. Thus, multiple piezoelectric filterelements (collectively 30) can be assembled and electrically connectedinto a filter system and can be controlled by and disposed on a commonelectronic circuit 22.

In operation, a voltage is supplied across the top and bottom electrodes32T, 32B, for example through electrical conductors 40 in electricalcontact with the top and bottom electrodes 32T, 32B. The suppliedvoltage forms an electrical field that causes the piezoelectric filterelement 30 to contract or expand. When the voltage is supplied at afrequency corresponding to a pre-determined size of the piezoelectricfilter element 30, a transverse acoustic wave 62 is formed in thepiezoelectric filter element 30 between the left and right acousticmirrors 35L, 35R. The transverse acoustic waves 62 are reinforcedthrough constructive interference at resonant frequencies in thepiezoelectric filter element 30 and destructively interferes at othernon-resonant frequencies, forming a resonant acoustic wave and therebyproviding a mechanical filter that transforms, through the piezoelectricmaterial, an input variable electrical signal to a filtered outputelectrical signal.

In some embodiments, the acoustic waves between the front and back sides30F, 30K and between the top and bottom sides 30T, 30M alsodestructively interfere so that only resonant frequencies between theleft and right acoustic mirrors 35L, 35R are reinforced. However, inother embodiments, for example in which the front and back acousticmirrors 35F, 35K are provided, resonant acoustic waves are also formedin the piezoelectric filter element 30 between the front and backacoustic mirrors 35F, 35K. The resonant acoustic waves between the frontand back acoustic mirrors 35F, 35K can be at the same frequencies as theresonant acoustic waves between the left and right acoustic mirrors 35L,35R, or can be at different frequencies.

In some embodiments in which the top and bottom acoustic mirrors 35T,35M are provided, resonant acoustic waves are also formed in thepiezoelectric filter element 30 between the top and bottom acousticmirrors 35T, 35M. The resonant acoustic waves between the top and bottomacoustic mirrors 35T, 35M can be at the same frequencies as the resonantacoustic waves between the left and right acoustic mirrors 35L, 35R, orcan be at different frequencies.

In some embodiments in which the top and bottom acoustic mirrors 35T,35M and the front and back acoustic mirrors 35F, 35K are provided,resonant acoustic waves are also formed in the piezoelectric filterelement 30 between the top and bottom acoustic mirrors 35T, 35M and thefront and back acoustic mirrors 35F, 35K. The resonant acoustic wavesbetween the top and bottom acoustic mirrors 35T, 35M and the front andback acoustic mirrors 35F, 35K can be at the same frequencies as theresonant acoustic waves between the left and right acoustic mirrors 35L,35R, or can be at different frequencies.

Acoustic mirrors (for example, 35L and 35R) can be formed on theelectrode 32 or on the piezoelectric layer 30 or both and can bepatterned, if desired, using photolithographic processes. An acousticmirror 35 of a transverse bulk acoustic wave filter 71 can includesub-layers, for example alternating layers of low-impedance (e.g.,dielectric) and high-impedance (e.g., metal) reflector layers (forexample quarter-wave thickness) chosen to constructively anddestructively interfere with the acoustic waves generated in the filterlayer 30 and thereby improve the performance of the acoustic wave filter70. The different layers of an acoustic mirror can transmit sound wavesat different velocities, enabling constructive and destructiveinterference of the sound waves at frequencies depending on the relativethicknesses and sound velocities of the materials within the one or moresub-layers.

Referring to FIG. 19, in embodiments of the present invention, atransverse acoustic wave filter wafer 27 comprises a source wafer 29comprising substrate material. A patterned sacrificial layer 28 formssacrificial portions 28 on, over, or in the substrate material, asurface of the substrate material, the source wafer 29, or a surface ofthe source wafer 29. The sacrificial portions 28 define separate anchors92 between the sacrificial portions 28. At least one transverse bulkacoustic wave filter 71 is disposed entirely over each sacrificialportion 28. The bottom electrode 32B adjacent to the sacrificial portion28 can have a protective dielectric layer 52. In some embodiments, thesacrificial portion 28 is etched to form a gap between the transversebulk acoustic wave filter 71 and the source wafer 29 and a tether 94physically connecting the transverse bulk acoustic wave filter 71 to ananchor 92. A transverse bulk acoustic wave filter 71 can be connected toan anchor 92 by one or more tethers 94.

In some embodiments of the present invention, the transverse bulkacoustic wave filter 71 is micro-transfer printed from the source wafer29 (FIG. 19) to an adhesive layer 50 on a device wafer 80 (as shown inFIG. 20). The device wafer 80 comprises, as did the original sourcewafer 29, a substrate material with a patterned sacrificial layer 28forming sacrificial portions 28 on, over, or in the substrate material,a surface of the substrate material, the device wafer 80, or a surfaceof the device wafer 80. The sacrificial portions 28 define separateanchors 92 between the sacrificial portions 28. The transverse bulkacoustic wave filter 71 is disposed entirely over the sacrificialportion 28. The device wafer 80 is processed to form electricalconductors 40, for example extending through a via in the adhesivesubstrate 50 to expose circuit connection pads 24. The device wafer 80can comprise a semiconductor layer or substrate 20 having an activeelectronic circuit 22 to which the transverse bulk acoustic wave filter71 is adhered by the adhesive layer 50 and to which the electricalconductors 40 are electrically connected through the circuit connectionpads 24. Thus, the transverse bulk acoustic wave filter 71 can becontrolled by the electronic circuit 22 to form a very small integratedheterogeneous compound acoustic wave filter device 10 with reducedthickness that can include multiple filter elements 30. The compoundacoustic wave filter device 10 itself can be micro-transfer printed fromthe device wafer 80 by etching the sacrificial portions 28 to suspend orposition the compound acoustic wave filter device 10 over the devicewafer 80 by the tether 94. In some embodiments, more than one tether isused. Using a stamp to separate and, in some embodiments, fracture thetether 94, the compound acoustic wave filter device 10 is adhered to thestamp and transferred to a destination substrate 82, as shown in FIG.21.

Referring to FIG. 21, piezoelectric filter elements 30 have beenconstructed and two of the piezoelectric filter elements 30 are shownwith the top side 30T visible. In the left micro-graph of FIG. 21, thepiezoelectric filter elements 30 are attached to a source wafer 29 witha tether 94. In the center micro-graph of FIG. 21, the piezoelectricfilter elements 30 are released from the source wafer 29 and suspendedover the source wafer 29 with the tether 94. In the right micro-graph ofFIG. 21, the piezoelectric filter elements 30 are printed onto adestination substrate 82. The length L of various samples of thepiezoelectric filter elements 30 is between 190 and 270 microns and thewidth W is 45 to 75 microns. The piezoelectric filter element 30thickness H is 0.5 microns in every case, excluding the top electrode32T.

Embodiments of the compound acoustic wave filter device 10 of thepresent invention integrate substrates made of different materials, forexample, different semiconductor materials or a semiconductor materialand a ceramic. Such integrations of different substrate materials areheterogeneous and combine structures including different types ofelements or different materials (particularly substrate materials) in acompound structure. For example, referring to FIGS. 1A, 1B, and 2,methods and structures of the present invention can include a firstsubstrate 20 comprising a first material. An active first circuit 22 isformed in or on the first substrate 20, the active first circuit 22including one or more first connection pads 24 connected to the activefirst circuit 22 for providing signals to the active first circuit 22 orreceiving signals from the active first circuit 22. A second substrate30 separate, distinct, and independent from the first substrate 20includes a second material different from the first material and ismounted on the first substrate 20 using, for example, micro-transferprinting. The electrodes 32 or a second circuit is formed in or on thesecond substrate 30 and includes one or more second connection pads 34connected to the electrodes 32 for providing signals to the electrodes32 or second circuit or receiving signals from the electrodes 32 orsecond circuit. One or more electrical conductors 40 electricallyconnect one or more of the first connection pads 24 to one or more ofthe second connection pads 34. In other embodiments, a plurality of theelectrodes 32 or second circuits are formed on or in the secondsubstrate 30 and the first connection pads 24 are connected to thesecond connection pads 34 of the plurality of electrodes 32 with the oneor more electrical conductors 40. Alternatively, a heterogeneous deviceof the present invention includes a plurality of the separate, distinct,and independent second substrates 30 mounted on the first substrate 20and the first connection pads 24 are connected to the second connectionpads 34 of the plurality of second substrates 30 with the one or moreelectrical conductors 40.

In an embodiment of the present invention, the one or more electricalconductors 40 are electrically conductive protrusions or spikesextending from the second substrate 30 in electrical contact with thefirst connection pads 24.

In an embodiment of the present invention, the second substrate 30 ismounted directly on or adhered directly to the first substrate 20 or onthe active first circuit 22 formed on or in the first substrate 20.Thus, the active first circuit 22 can be located at least partiallybetween the second substrate 30 and at least portions of the firstsubstrate 20. The second substrate 30 can be adhered to the firstsubstrate 20 with a layer 50 of adhesive, for example a curable adhesivesuch as SU8. The first substrate 20 can include multiple layers ofdifferent materials, either patterned or unpatterned.

The first or second substrates 20, 30 can be chiplets, small integratedcircuits or processed substrates suitable for micro-transfer printing.In various embodiments, the first substrate 20 or the second substrate30 has a width from 2 to 5 μm, 5 to 10 μm, 10 to 20 μm, or 20 to 50 μm,the first substrate 20 or the second substrate 30 has a length from 2 to5 μm, 5 to 10 μm, 10 to 20 μm, or 20 to 50 μm, or the first substrate 20or the second substrate 30 has a height from 2 to 5 μm, 4 to 10 μm, 10to 20 μm, or 20 to 50 μm. Such small substrate elements provide a highdegree of integration and consequently reduced manufacturing costs andincreased performance.

A method of making a heterogeneous device similar to the methodillustrated in FIG. 5 includes: providing a first substrate 20 with anactive first circuit 22 formed in or on the first substrate 20, theactive first circuit 22 including one or more first connection pads 24connected to the active first circuit 22 for providing signals to theactive first circuit 22 or receiving signals from the active firstcircuit 22 in step 105. A second substrate 30 separate, distinct, andindependent from the first substrate 20 having electrodes 32 or a secondcircuit formed in or on the second substrate 30 and one or more secondconnection pads 34 connected to the electrodes 32 for providing signalsto or receiving signals from the second circuit is provided in step 125.Adhesive is provided between the first and second substrates 20, 30 instep 140, the second substrate 30 is mounted upon the first substrate 20in step 150 (e.g., by micro-transfer printing), and one or more of thefirst connection pads 24 is electrically connected to one or more of thesecond connection pads 34 in step 170.

In further embodiments, step 130 provides a plurality of the electrodes32 or second circuits on the second substrate 30 and the one or moresecond connection pads 34 of each of the second circuits areelectrically connected to the one or more first connection pads 24.Alternatively, or in addition, a plurality of second substrates 30 isprovided and the plurality of second substrates 30 is mounted on thefirst substrate 20 using micro-transfer printing (step 150). One or moreof the second connection pads 34 of each of the second substrates 30 areelectrically connected to one or more of the first connection pads 24 toelectrically connect the active first circuit 22 to the electrodes 32 orthe second circuit (step 170). The second substrate 30 can be adhered tothe first substrate 20 by disposing an adhesive layer 50 in step 140between the first and second substrates 20, 30 and curing the layer 50of adhesive, if necessary, in step 160.

In a further embodiment, the second connection pads 34 are electricallyconductive protrusions or spikes extending from the second substrate 30and the second substrate 30 is mounted on the first substrate 20 bypressing the electrically conductive protrusions or spikes against orinto the first connection pads 24 (e.g., by micro-transfer printing) toform an electrical connection between the second circuit and the activefirst circuit 22 so that the electrically conductive protrusions orspikes form the one or more electrical conductors 40. As noted above, anadhesive layer 50 or patterned adhesive layer 50 can be used incombination with the conductive protrusions or spikes to provideelectrical connections and adhesion between the first substrate 20 andsecond substrate 30.

In operation, the compound acoustic wave filter device 10 orheterogeneous device 10 is operated by providing electrical signals froma controller (not shown) through circuit (first) connection pads 24 toactivate the active electronic (first) circuit 22 on the semiconductor(first) substrate 20. The active electronic (first) circuit 22 canfurther process the signals or communicate the signals, or both, to theelectrodes 32 or second circuit on the filter (second) substrate 30through the circuit (first) connection pads 24, the electrical conductor40, and the filter (second) connection pads 34. The electrodes 32communicate or the second circuit processes the communicated signals andprovides the processed signal through the filter (second) connectionpads 34, the electrical conductors 40, and the circuit (first)connection pads 24 to the active electronic (first) circuit 22. Theactive electronic (first) circuit 22 can further process the signals andenable actions or communicate the signals to the controller.

A plurality of the electrodes 32 can be made in an acoustic wave filterwafer 12 comprising the material of the filter element 30. As shown inFIG. 9K, sacrificial layers 28 or sacrificial portions 28, tethers 94,and anchors 92 can be formed between the electrodes 32 and the acousticwave filter wafer 12 to form individual filter elements 30, each filterelement 30 having one or more electrodes 32, and render the filterelements 30 micro-transfer printable. Similarly, an array of the activeelectronic circuits 22 can be made in a crystalline semiconductor wafer,for example, a silicon wafer such as silicon (1 0 0) or silicon (1 1 1).The filter elements 30 can be micro-transfer printed on thesemiconductor substrates 20 (the semiconductor wafer) and the electrodes32 and active electronic circuit 22 electrically connected with theelectrical conductors 40. The integrated micro-transfer printed assemblycan be used in a system as it is or the semiconductor wafer can be dicedand optionally packaged, for example to form surface-mount devices, anddisposed as desired in a system. Alternatively, sacrificial layers orsacrificial portions 28, tethers 94, and anchors 92 can be formedbetween the active electronic circuit 22 and the semiconductor wafer toform individual semiconductor substrates 20 and render the activeelectronic circuit 22 and electrode 32 assemblies micro-transferprintable. The compound filter or heterogeneous devices 10 of thepresent invention can then be micro-transfer printed as desired in asystem.

U.S. patent application Ser. No. 14/743,981, filed Jun. 18, 2015,entitled Micro Assembled LED Displays and Lighting Elements,incorporated herein by reference describes micro-transfer printingstructures and processes useful with the present invention. For adiscussion of micro-transfer printing techniques see, U.S. Pat. Nos.8,722,458, 7,622,367 and 8,506,867, each of which is hereby incorporatedby reference in its entirety. Micro-transfer printing using compoundmicro assembly structures and methods can also be used with the presentinvention, for example, as described in U.S. patent application Ser. No.14/822,868, filed Aug. 10, 2015, entitled Compound Micro-AssemblyStrategies and Devices, which is hereby incorporated by reference in itsentirety.

As is understood by those skilled in the art, the terms “over”, “under”,“above”, “below”, “beneath”, and “on” are relative terms and can beinterchanged in reference to different orientations of the layers,elements, and substrates included in the present invention. For example,a first layer on a second layer, in some embodiments means a first layerdirectly on and in contact with a second layer. In other embodiments, afirst layer on a second layer can include another layer there between.Additionally, “on” can mean “on” or “in.” As additional non-limitingexamples, a sacrificial layer or sacrificial portion 28 is considered“on” a substrate when a layer of sacrificial material or sacrificialportion 28 is on top of the substrate, when a portion of the substrateitself is the sacrificial layer 28, or when the sacrificial layer orsacrificial portion 28 comprises material on top of the substrate and aportion of the substrate itself.

Having described certain embodiments, it will now become apparent to oneof skill in the art that other embodiments incorporating the concepts ofthe disclosure may be used. Therefore, the invention should not belimited to the described embodiments, but rather should be limited onlyby the spirit and scope of the following claims.

Throughout the description, where apparatus and systems are described ashaving, including, or comprising specific components, or where processesand methods are described as having, including, or comprising specificsteps, it is contemplated that, additionally, there are apparatus, andsystems of the disclosed technology that consist essentially of, orconsist of, the recited components, and that there are processes andmethods according to the disclosed technology that consist essentiallyof, or consist of, the recited processing steps.

It should be understood that the order of steps or order for performingcertain action is immaterial so long as the disclosed technology remainsoperable. Moreover, two or more steps or actions in some circumstancescan be conducted simultaneously. The invention has been described indetail with particular reference to certain embodiments thereof, but itwill be understood that variations and modifications can be effectedwithin the spirit and scope of the invention.

PARTS LIST

-   A cross section line-   H height/thickness-   L length-   W width-   10 compound acoustic wave filter device/heterogeneous device-   12 acoustic wave filter wafer/source wafer-   20 support substrate/semiconductor substrate/first substrate-   21 support substrate area-   22 active electronic circuit/first circuit-   23 active electronic circuit area-   24 circuit connection pad/first connection pad-   25 semiconductor material-   26 process side-   27 transverse acoustic wave filter wafer-   28 sacrificial layer/sacrificial portion-   29 handle wafer/source wafer-   30 filter element/piezoelectric layer/piezoelectric filter/filter    layer/filter substrate/second substrate-   30A filter element-   30B filter element-   30C filter element-   30D filter element-   30F filter element front side-   30K filter element back side-   30L filter element left side-   30R filter element right side-   30M filter element bottom side-   30T filter element top side-   31 filter element area-   32 electrode-   32B bottom electrode-   32T top electrode-   34 filter connection pad/second connection pad-   35 acoustic mirror/acoustic mirror layer-   35F front acoustic mirror-   35K back acoustic mirror-   35L left acoustic mirror-   35R right acoustic mirror-   35M bottom acoustic mirror-   35T top acoustic mirror-   36 transducer/first transducer-   38 second transducer-   39 support wafer-   40 electrical conductor-   50 adhesive layer-   52 dielectric layer-   54 adhesive layer/resin layer-   60 acoustic wave-   62 transverse acoustic wave-   70 acoustic wave filter-   70A acoustic wave filter-   70B acoustic wave filter-   70C acoustic wave filter-   70D acoustic wave filter-   71 transverse bulk acoustic wave filter-   78 surface-mount device-   80 device wafer-   82 destination substrate-   90 optional buffer layer-   92 anchor-   94 tether-   100 provide substrate step-   105 provide semiconductor substrate with electronic circuit step-   110 form electronic circuit on semiconductor substrate step-   120 provide source wafer step-   125 provide acoustic filter on source wafer step-   130 form acoustic filter on source wafer step-   140 dispose adhesive material step-   150 micro-transfer print acoustic filter on semiconductor substrate    step-   170 connect electronic circuit to filter circuit step-   160 optional cure adhesive layer step-   180 optional micro-transfer print integrated assembly step-   200 provide support wafer step-   202 provide source wafer/handle wafer step-   205 optional form buffer layer step-   210 form piezoelectric layer step-   220 form electrode on piezoelectric layer step-   225 optional form acoustic mirror layer step-   230 form patterned sacrificial layer step-   240 form adhesive layer step-   250 adhere semiconductor substrate to adhesive layer step-   260 remove support wafer step-   270 form electrode on piezoelectric layer step-   275 optional form acoustic mirror layer step-   280 etch patterned sacrificial layer step

What is claimed:
 1. A transverse bulk acoustic wave filter, comprising:a piezoelectric filter element having a top side, a bottom side, a leftside, and a right side, wherein the right side is opposed to the leftside and the bottom side is opposed to the top side; a top electrode incontact with the top side; a bottom electrode in contact with the bottomside; a left acoustic mirror in contact with the left side; and a rightacoustic mirror in contact with the right side.
 2. The transverse bulkacoustic wave filter of claim 1, wherein the piezoelectric filterelement has a front side and a back side, and comprising: a frontacoustic mirror in contact with the front side; and a back acousticmirror in contact with the back side.
 3. The transverse bulk acousticwave filter of claim 1, comprising: a bottom acoustic mirror in contactwith the bottom electrode and, optionally, in contact with at least aportion of the bottom side.
 4. The transverse bulk acoustic wave filterof claim 1, comprising: a top acoustic mirror in contact with the topelectrode and, optionally, in contact with at least a portion of the topside.
 5. The transverse bulk acoustic wave filter of claim 1, whereinthe distance between the top side and the bottom side is less than thedistance between the left side and the right side or is less than orequal to one half, one quarter, one tenth, one twentieth, one fiftieth,1/100, or 1/200 of the distance between the left side and the rightside.
 6. The transverse bulk acoustic wave filter of claim 1, whereinthe piezoelectric filter element has a front side and a back side, andwherein the distance between the top side and the bottom side is lessthan the distance between the front side and the back side or is lessthan or equal to one half, one quarter, one tenth, one twentieth, onefiftieth, 1/100, or 1/200 of the distance between the front side and theback side.
 7. The transverse bulk acoustic wave filter of claim 6,wherein the distance between the front side and the back side is lessthan the distance between the left side and the right side or is lessthan or equal to one half, one third, one quarter, one tenth, or onetwentieth of the distance between the left side and the back side. 8.The transverse bulk acoustic wave filter of claim 1, wherein a crosssection of the piezoelectric filter element is substantiallyrectangular.
 9. The transverse bulk acoustic wave filter of claim 1,wherein a voltage applied across the top and bottom electrodes forms aresonant acoustic wave in the piezoelectric filter element between theleft and right acoustic mirrors.
 10. The transverse bulk acoustic wavefilter of claim 9, wherein the piezoelectric filter element has a frontside and a back side, the transverse bulk acoustic wave filter comprisesa front acoustic mirror in contact with the front side and a backacoustic mirror in contact with the back side, and wherein the appliedvoltage forms a resonant acoustic wave in the piezoelectric filterelement between the front and back acoustic mirrors.
 11. The transversebulk acoustic wave filter of claim 9, wherein the piezoelectric filterelement has a top acoustic mirror in contact with the top electrode anda bottom acoustic mirror in contact with the bottom electrode andwherein the applied voltage forms a resonant acoustic wave in thepiezoelectric filter element between the top and bottom acousticmirrors.
 12. The transverse bulk acoustic wave filter of claim 1,comprising a top electrical conductor in electrical contact with the topelectrode and a bottom electrical conductor in contact with the bottomelectrode, and wherein the top electrical conductor is disposed at leastpartially on, in, or as part of the left acoustic mirror and the bottomelectrical conductor is disposed at least partially on, in, or as partof the right acoustic mirror, or wherein the top electrical conductor isinsulated from the left side by a dielectric structure that forms atleast a portion of the left acoustic mirror and the bottom electricalconductor is insulated from the right acoustic mirror by a dielectricstructure that forms at least a portion of the right acoustic mirror.13. The transverse bulk acoustic wave filter of claim 1, comprising afractured or separated tether.
 14. The transverse bulk acoustic wavefilter of claim 1, comprising a support substrate comprising top andbottom circuit connection pads and wherein the bottom electrode isadhered to the support substrate, the top circuit connection pad iselectrically connected to the top electrode, and the bottom circuitconnection pad is electrically connected to the bottom electrode. 15.The transverse bulk acoustic wave filter of claim 14, wherein thesupport substrate is a semiconductor substrate and further comprising anactive electronic circuit formed in or on the semiconductor substrate,the active electronic circuit electrically connected to the top andbottom circuit connection pads.
 16. The transverse bulk acoustic wavefilter of claim 15, wherein the active electronic circuit is disposed atleast partially between the piezoelectric filter element and the supportsubstrate.
 17. The transverse bulk acoustic wave filter of claim 1,wherein the piezoelectric filter element is a first piezoelectric filterelement and comprising a second piezoelectric filter element, whereinthe second piezoelectric filter element has a top side and a bottom sideopposed to the top side and a left side and a right side opposed to theleft side, a top electrode in contact with the top side, a bottomelectrode in contact with the bottom side, a left acoustic mirror incontact with the left side, and a right acoustic mirror in contact withthe right side; and wherein the top and bottom electrodes of the secondpiezoelectric filter element are electrically connected to the activeelectronic circuit.
 18. The transverse bulk acoustic wave filter ofclaim 1, wherein at least one of the left acoustic mirror and rightacoustic mirror comprises a plurality of alternating high-impedance andlow-impedance sub-layers.
 19. A transverse acoustic wave filter wafer,comprising: a source wafer comprising substrate material; a patternedsacrificial layer forming sacrificial portions on, over, or in thesubstrate material, a surface of the substrate material, the sourcewafer, or a surface of the source wafer, the sacrificial portionsdefining separate anchors between the sacrificial portions; and atransverse bulk acoustic wave filter according to claim 1 disposedentirely over each sacrificial portion.
 20. A transverse acoustic wavefilter wafer, comprising: a device wafer comprising substrate material;a patterned sacrificial layer forming sacrificial portions on, over, orin the substrate material, a surface of the substrate material, thedevice wafer, or a surface of the device wafer, the sacrificial portionsdefining separate anchors between the sacrificial portions; a transversebulk acoustic wave filter disposed entirely over each sacrificialportion, the transverse bulk acoustic wave filter comprising apiezoelectric filter element having a top side, a bottom side, a leftside, and a right side, wherein the right side is opposed to the leftside and the bottom side is opposed to the top side, a top electrode incontact with the top side, a bottom electrode in contact with the bottomside, a left acoustic mirror in contact with the left side, a rightacoustic mirror in contact with the right side, and a fractured orseparated tether; and an electrical connection electrically connected tothe top electrode and an electrical connection electrically connected tothe bottom electrode.
 21. The acoustic wave filter wafer of claim 20,comprising a semiconductor layer disposed entirely over each sacrificialportion between the sacrificial portion and the transverse bulk acousticwave filter, the semiconductor layer comprising an active electroniccircuit to which the electrical connections are electrically connected.